Sciei 


SCIENCE  FOR 
BEGINNERS 

FALL 


NEW-WORLD     SCIENCE    SERIES 
Edited  by  John   W.  Ritchie 

SCIENCE  FOR 
BEGINNERS 

A  First  Book  in  General  Science 

for  Intermediate  Schools  and 

Junior  High  Schools 

by 

DELOS    FALL,    D.Sc. 

Professor  of  Chemistry,  Albion  College 

Formerly  Michigan  State  Superintendent 

of  Public  Instruction 

ILLUSTRATED    BT 

Will  H.    Schanck  and  Elliott  Dold 


Tonkers-on-Hudson>  New  York 

WORLD  BOOK  COMPANY 

1917 


WORLD    BOOK    COMPANY 

THE   HOUSE   OF   APPLIED   KNOWLEDGE 
Established,  1905,  by  Caspar  W.  Hodgson 

YONKERS-ON-HUDSON,  NEW  YORK 
2126   PRAIRIE   AVENUE,  CHICAGO 


The  purpose  of  this  house  is  to  publish  books 
that  apply  the  world's  knowledge  to  the  world's 
needs.  Texts  in  science  offer  unusual  opportu- 
nities for  the  realization  of  such  a  purpose,  and  it 
is  intended  that  each  volume  of  the  New-World 
Science  Series  shall  be  a  concrete  expression  of 
this  ideal  of  educational  service.  Editor  and 
publisher  take  pleasure  in  offering  for  use  in 
intermediate  schools  and  junior  high  schools 
Fall's  Science  for  Beginners,  the  first  book  of  the 
series,  and  announce  that  other  volumes  for  use 
in  junior  high  schools,  high  schools,  and  colleges 
will  follow 


NWSS  :  FSB-I 


Copyright,  1917,  by  World  Book  Company 
All  rights  reserved 


PREFACE 

ONLY  a  generation  ago,  it  was  the  prevailing  idea  that  all 
instruction  in  schools  and  all  learning  by  pupils  should  be 
confined  to  the  schoolroom  and  to  books.  Nature  study 
was  unknown,  except  that  once  in  a  while  curious  relics  from 
foreign  countries  were  brought  in  to  emphasize  some  phase 
of  the  pupil's  study.  A  little  later  more  material  was  taken 
into  the  classes  and  used  to  verify  to  some  extent  the  state- 
ments of  the  books.  But  these  were  only  fragments  of  the 
part  of  nature  which  they  represented,  and  for  that  reason 
aroused  very  little  interest  in  either  teacher  or  pupil.  Out  of 
this  somewhat  fragmentary  study  has  grown  the  laboratory 
method  which  is  used  in  the  better  schools  at  the  present 
time.  But  even  yet  there  is  not  enough  use  of  the  real 
thing  and  the  whole  thing.  The  material  for  study  is 
gathered  by  the  teacher  or  is  furnished  by  the  school  authori- 
ties, and  the  pupils  are  required  to  handle  only  those  portions 
which  will  illustrate  the  point  under  discussion. 

Gradually,  however,  teachers  are  coming  to  see  that  to  get 
the  best  results  the  pupil  must,  whenever  possible,  gather 
his  own  material.  When  this  point  is  conceded,  it  is  readily 
agreed  that  the  pupil  may  oftentimes  study  his  materials  to 
greater  advantage  in  their  natural  environment.  The  in- 
evitable conclusion  to  be  drawn  from  all  such  reasoning  is 
that  in  many  cases  the  study  of  nature  requires  that  the 
pupil  should  go  out  of  doors  and,  under  proper  guidance, 
observe,  examine,  describe,  reason  upon,  and  finally  draw 
his  own  conclusions  concerning  the  matter  in  hand. 

It  is  suggested  that  the  less  help  the  pupil  has  the  better 
he  will  do  his  work,  provided  he  is  given  necessary  instruc- 
tions and  encouraged  to  go  on  to  the*  end  of  his  study.  After 
he  has  exhausted  his  own  resources  in  a  given  problem,  it  is 
the  teacher's  part  to  contribute  by  supplementing  and  en- 
riching the  knowledge  which  has  been  obtained  by  the  pupil. 

iii 

376360 


iv  Preface 

But  until  the  work  of  the  pupil  is  done,  the  role  of  the  teacher 
should  be  one  of  masterful  inactivity. 

The  teacher  is  asked  to  keep  in  mind  that  the  chief  purpose 
of  this  book  is  not  to  give  the  pupils  a  large  amount  of 
information,  but  rather  to  introduce  them  to  a  method 
through  the  use  of  which  they  will  acquire  the  habit  of  gain- 
ing information  for  themselves.  The  scientific  method,  by 
which  is  meant  that  methodical  procedure  which  is  more  and 
more  coming  to  be  used  in  all  lines  of  human  activity,  is  most 
easily  applied  in  the  field  of  the  natural  sciences,  and  the 
pupil  can  best  learn  the  method  of  the  scientist  by  using  the 
material  with  which  the  scientist  works. 

The  author  makes  no  apology  for  the  constant  use  of  the 
direct  address.  The  book  is  a  direct  message  to  the  user  of 
it,  and  it  is  to  be  hoped  that  the  teacher  will  encourage  the 
idea  that  here  is  the  boy's  and  the  girl's  own  book. 

For  helpful  suggestions  the  author  is  under  obligations  to 
Miss  Marie  K.  Dunn,  Teacher  of  Science,  Junior  High 
School,  Solvay,  New  York;  Donald  P.  Boyer,  Principal 
Bellevue  Junior  High  School,  Richmond,  Virginia ;  Stanley 
S.  Foote,  Lincoln  Intermediate  School,  Santa  Monica,  Cali- 
fornia ;  Harry  A.  Richardson,  Teacher  of  General  Science, 
Junior  High  School,  Kalamazoo,  Michigan ;  Professor  William 
J.  Bray,  First  District  Normal  School,  Kirksville,  Missouri; 
and  Dr.  Albert  Leonard,  Superintendent  of  Schools,  New 
Rochelle,  New  York ;  each  of  whom  read  the  manuscript  in 
its  original  form.  He  is  also  indebted  to  Professors  Clarence 
W.  Greene  and  Frank  W.  Douglas,  Albion  College,  and  to 
Professor  William  H.  Keeble,  College  of  William  and  Mary, 
for  valuable  aid  in  the  preparation  of  the  chapters  dealing 
with  physical  subjects,  and  to  Dr.  William  C.  Bagley,  of 
Teachers  College,  Columbia  University,  for  reading  the  dis- 
cussion of  the  scientific  method  found  in  the  opening  chapters. 


CONTENTS 

CHAPTER  PAGE 

I.  SCIENCE  AND  THE  SCIENTIFIC  METHOD        .        .   .     i 

II.  WHAT  THE  YOUNG  SCIENTIST  MUST  LEARN  TO  Do      12 

III.  MATTER  AND  ITS  FORMS 22 

IV.  SOME  PROPERTIES  OF  MATTER     .        .        .        .28 
V.     CHANGES  IN  MATTER 37 

VI.  OXYGEN  :   THE  ACTIVE  ELEMENT  ....      44 

VII.  HYDROGEN  AND  ITS  COMPOUNDS  .        .        .        .51 

VIII.    A  STUDY  OF  WATER 60 

IX.    A  PINCH  OF  SALT 72 

X.     CHLORIN  AND  SODIUM 83 

XI.    A  STUDY  OF  A  MATCH 92 

XII.  CARBON  AND  ITS  COMPOUNDS      .        .        .        .100 

XIII.  A  CAKE  OF  SOAP 112 

XIV.  A  LOAF  OF  BREAD 124 

'XV.  THE  LIMESTONE  STORY         ...        .        .139 

XVI.  A  FIELD  EXCURSION  FOR  MINERALS    .        .        .149 

XVII.    LOOKING  FOR  ROCKS 155 

XVIII.    THE  SOIL 165 

XIX.    THE  POTATO 175 

XX.    A  STUDY  OF  THE  AIR 186 

XXI.    THE  WEATHER 198 

XXII.    MATTER  AND  MOTION 217 

XXIII.  MOTION  To  AND  FRO 228 

XXIV.  SOUND 235 

XXV.  HEAT     .        .        .        .        .        .        .        .        .242 

XXVI.  How  TO  MEASURE  TEMPERATURES      .        .        .252 


vi  Contents 

CHAPTER  PAGE 

XXVII.  PRACTICAL  THERMOMETRICAL  PROBLEMS    .        .  265 

XXVIII.    THE  PHOTOGRAPH 271 

XXIX.    THE  LIGHT 282 

XXX.  THE  MARINER'S  COMPASS          ....  300 

XXXI.     ELECTRICITY 308 

XXXII.     ELECTRICITY  (Continued) 323 

XXXIII.  WORK  AND  ENERGY 337 

XXXIV.  AIDS  TO  OUR  WORK 349 

APPENDIX:  TABLE  OF  ELEMENTS 371 

INDEX  373 


TO   THE   BOYS   AND    GIRLS   WHO   USE 
THIS   BOOK 

THE  writer  of  this  book  remembers  very  clearly  that 
in  his  boyhood  days  he  had  an  intense  desire  to  investi- 
gate those  things  that  were  immediately  about  him.  He 
had  a  dim  notion  that  the  problems  of  everyday  life 
would  prove  most  interesting  if  they  could  be  solved  in 
some  way  by  himself.  To  him  it  seemed  far  more 
captivating  to  obtain  knowledge  through  his  own  experi- 
ments than  by  merely  reading  from  a  book.  This 
thought  has  remained  with  him  all  through  the  years, 
and  it  is  because  of  it  that  this  book  has  been  written ; 
the  purpose  has  been  to  provide  a  book  that  will  permit 
you  to  get  the  information  for  yourself. 

The  writer  confesses  one  great  anxiety,  however. 
Will  you,  the  boys  and  girls  who  use  this  book,  have  the 
courage  to  carry  on  the  work  in  accordance  with  the 
spirit  of  the  book?  Will  you  do  the  work  for  your- 
selves, make  the  observations,  keep  a  notebook,  and 
so  learn  to  know  by  doing  ? 

If  you  desire  to  secure  the  best  results  from  the  use  of 
this  book,  or  any  book  for  that  matter,  you  must  have  a 
well-laid-out  plan  and  must  not  do  your  work  in  the 
haphazard  way  that  is  characteristic  of  many  boys  and 
girls  of  your  age.  You  are  asked  to  study  carefully  the 
suggestions  that  follow,  and,  if  you  think  them  worth 
adopting,  to  observe  them  to  the  best  of  your  ability. 

1.  Make  out  a  definite  daily  program  for  every  hour 
of  the  day,  and  especially  the  exact  time  that  you  will 
devote  to  each  of  your  studies. 

2.  Provide  yourself  with  all  the  tools  you  will  need 


viii    To  the  Boys  and  Girls  Who  Use  this  Book 

for  the  prosecution  of  your  work,  —  textbook,  notebook, 
pencil,  eraser,  practice  paper  for  first  notes,  ruler,  and,  if 
possible,  a  good  dictionary. 

3.  Learn  to  make  the  best  use  of  your  textbook.     Give 
attention  to  chapter  and  paragraph  headings,  to  words 
that  are  marked  with  a  star,  and  to  statements  that  are 
underscored.     Examine  the  pictures  carefully.     Every 
one  of  them  teaches  some  important  truth.     Use  the 
index,  give  attention  to  footnotes,  and  study  out  the 
meaning  of  the  design  on  the  cover.      How  to  use  a 
book  is  an  art  that  you  should  learn. 

4.  Study  by  yourself.     Solve  your  own  problems  and 
do  your  own  thinking;    for  in  this  way  only  will  you 
grow  as  a  scholar. 

5.  Studying  is  simply  intensified  reading.     Therefore 
learn  to  read  in  such  a  way  as  to  get  the  real  thought. 
"One   hour's   bright,  wide-awake,    concentrated,  inter- 
ested study  is  worth  a  day's  plodding." 

6.  Find  and  state  the  problems  in  the  subject  you  are 
studying.     You  are  well  on  the  way  to  knowledge  when 
you  know  exactly  what  you  want  to  know. 

7.  Never  ask  another  person  to  answer  a  question  if 
by  thinking  you  can  answer  it  for  yourself;   but  never 
go  without  a  necessary  bit  of  knowledge  that  you  can 
gain  by  asking  a  question. 

8.  Learn  to  use  the  method  of  experiment  in  order  to 
find  answers  to  many  questions  that  will  arise  in  your 
mind. 

9.  Remember  that  the  book  is  only  a  guide  to  show 
you  where  and  how  to  look  for  truth ;  and  remember  also 


To  the  Boys  and  Girls  Who  Use  this  Book     ix 

that  the  truth  is  hidden  away,  not  in  the  book,  but  in 
the  object  of  your  study.  What  that  truth  is,  you  must 
see  for  yourself.  It  would  be  unfortunate  for  you  if  the 
book  or  your  teacher  were  to  give  you  information  which 
by  observation  or  experiment  you  can  get  for  yourself. 

10.  Learn  to  use  all  your  senses ;   train  your  mind  to 
notice  what  your  eyes  see ;   train  your  ears  to  hear  and 
recognize  sounds;    train  your  hands  to  feel,  for  many 
times  they  are  far  better  than  your  eyes. 

11.  Give  attention  to  natural  objects  and  to  what  is 
happening  in  nature  about  you.     You  may  not  under- 
stand all  you  observe  just  now,  but  sometime  in  the 
future  what  you  are  now  seeing  will  become  a  valuable 
part  of  some  learning  process. 

12.  Think  about  what  you  have  learned.     Talk  it 
over  with  your   classmates   and  especially  with  your 
parents  or  older  brothers  and  sisters.     In  this  way  you 
will  bring  your  ideas  together  and  learn  the  answers  to 
questions  that  naturally  arise.     Thus  you  will  learn  to 
apply  your  knowledge  to  the  daily  experiences  of  life 
and  to  use  it  in  a  practical  way. 


SCIENCE  FOR  BEGINNERS 


CHAPTER   ONE 

SCIENCE  AND   THE  SCIENTIFIC   METHOD 


FIGS,  i  and  2.     Sometimes  you  can  find  the  answer   to   your  questions  by 
observation ;  sometimes  you  will  need  to  employ  the  method  of  experiment. 

THIS  is  a  book  in  elementary  science,  and  the  pupil 
who  uses  it  is  asked  to  be  a  scientist.  This  means  that 
he  must  work  as  a  scientist  works ;  think  as  a  scientist 
thinks ;  and  in  this  way  find  out  for  himself  some  of 
the  things  that  other  scientists  have  learned.  In  order 
that  he  may  begin  his  studies  in  the  right  way,  he 
should  know  what  science  is  and  how  a  scientist  goes 
about  his  work. 

What  science  is.  Science  is  defined  as  knowledge 
of  any  given  subject  properly  arranged  and  classified. 
A  person  may  know  a  great  many  facts  about  a  given 
thing,  but  if  his  knowledge  is  not  arranged  according 
to  some  system  or  plan  it  cannot  be  called  scientific 


2  Science  for  Beginners 

knowledge.  For  example,  an  Indian  may  know  the 
names  of  many  of  the  plants  that  grow  in  the  woods, 
when  and  where  to  look  for  them,  how  to  compound 
medicines  from  them,  and  when  their  fruits  will  be  ripe ; 
but  he  cannot  be  called  a  scientific  botanist,  partly  be- 
cause his  knowledge  is  not  extensive  enough,  but  more 
particularly  because  it  is  not  organized  and  because  his 
ideas  have  not  been  verified  by  exact  observation  and 
experiment.1 

The  scientific  habit.  In  using  this  book  you  will  often 
be  asked  to  make  observations  and  experiments,  and  to 
arrange  or  tabulate  in  an  orderly  manner  the  facts  that 
you  collect,  so  that  you  may  grow  into  what  may  be  called 
the  scientific  habit.  The  most  important  thing  that 
can  be  learned  from  a  study  of  science  is  the  method  of 
thinking  and  working  which  the  scientist  uses,  and  you 
will  be  asked  to  do  things  in  a  scientific  way  in  order  that 
you  may  learn  this  method.  Then  you  will  be  able  to 
apply  the  method  of  science  in  all  your  work  as  long  as 
you  live. 

The  scientific  method.  By  using  the  scientific  method 
you  can  answer  many  of  your  own  questions  without 
the  aid  of  a  teacher.  Sometimes  you  can  find  your  an- 
swers by  careful  observation ;  sometimes  you  will  find 
them  only  by  experiment.  By  one  or  the  other  of  these 
two  methods  men  of  science  have  made  all  their  inven- 
tions and  discoveries,  and  through  their  use  scientists 

1  Science  is  knowledge  gained  and  verified  by  exact  observation  and 
correct  thinking,  especially  as  methodically  formulated  and  arranged  in 
a  rational  system.  —  Standard  Dictionary. 


Science  and  the  Scientific  Method 


FIG.  3. 

are  every  day  asking  questions  of  Nature  and  receiving 
their  replies  from  her.  The  value  of  the  scientific 
method  lies  in  the  fact  that  it  enables  us  to  gain  new 
knowledge ;  by  its  use  we  can  get  information  for  our- 
selves without  the  aid  of  teachers  or  the  use  of  books. 

Illustrations  of  the  method.  An  understanding  of  the 
scientific  method  is  so  important  that  we  shall  give 
several  illustrations  of  how  it  is  used.  Suppose,  for 
example,  that  you  see  what  looks  like  a  load  of  wheat 
in  bags,  passing  your  house,  and  you  wonder  how  heavy 
the  load  is.  You  observe  that  the  bags  are  in  three 
rows  with  8  bags  in  a  row,  and  that  there  is  an  addi- 
tional bag  on  top  of  the  load.  How  many  bags  are 
there  ?  You  already  know  that  bags  of  this  kind  hold  2 
bushels.  How  many  bushels  are  in  the  load?  A 
bushel  of  wheat  weighs  60  pounds.  How  many  pounds 


4  Science  for  Beginners 

in  the  load?  A  ton  is  2000  pounds.  How  many  tons 
in  the  load  ? 

When  you  have  made  your  calculations,  you  have 
answered  the  question  for  yourself.  By  the  use  of  your 
eyes  and  your  mind,  you  have  learned  the  weight  of  the 
load  of  wheat. 

Steps  in  the  process.  In  working  out  a  problem  like  the 
above,  your  mind  goes  through  four,  and  sometimes  five, 


FIG.  4.     The  boys  wonder  what  the  FIG.  5.     They  make  their  observa- 

tortoise  weighs.  tions. 

separate  steps,  all  so  woven  into  each  other  that  they 
form  one  continuous  story.     These  steps  are  as  follows : 

(1)  Your  attention  is  attracted  to  some  unusual  object 
or  incident  and  you  wonder  what  it  is  or  what  it  is  all 
about;  you  are  curious  to  know ;  your  interest  is  aroused. 
This  is  the  first  step  in  starting  a  train  of  thought  in 
your  mind,  and  the  next  step  in  the  process  ought  to  be 
a  careful  examination  of  that  which  has  aroused  your 
curiosity. 

(2)  You  see  certain  things  with  your  eyes,  or  you  learn 
certain  facts  through  your  hearing  or  some  other  one  of 


Science  and  the  Scientific  Method  5 

your  senses.  This  step,  which  we  call  observation,  is 
the  most  important  step  of  all,  because  it  forms  the  basis 
of  what  follows.  What  you  are  observing  may  be  some- 
thing that  occurs  about  you  in  nature;  but  often  it 
will  be  necessary  to  make  an  experiment  and  watch  its 
progress,  in  order  to  get  the  facts  you  desire. 

(3)  You  quickly  recall  what  you  already  know  about 
the  thing  you  are  now  seeing  or  hearing.     You  have  seen 


FIG.  6.      They  recall  the  weights  of       FIG.  7.  They  conclude  that  the  tortoise 
different  objects.  probably  weighs  about  2  pounds. 

something  like  it  before  and  you  already  know  some 
facts  about  it.  These  facts  are  brought  together  and 
added  to  what  you  are  now  learning  by  observation. 
By  this  process  your  knowledge  of  the  object  is  en- 
larged and  enriched ;  and  a  more  thorough  observation 
might  furnish  you  with  other  facts  that  would  add  still 
more  to  your  knowledge  of  the  object. 

(4)  The  fourth  step  is  to  come  to  some  conclusion 
as  a  result  of  your  study ;  to  form  some  hypothesis,  or 


Science  for  Beginners 


theory,  that  will  explain  what  you  have  observed.  The 
conclusion,  or  hypothesis,  must  be  so  definite  that  it  can 
be  expressed  clearly.  Notice  that  the  more  accurate 
your  observations  have  been  and  the  more  you  are  able 
to  add  to  them  from  previous  experiences,  the  more  defi- 
nite and  clear  will  be  the  conclusion  you  are  able  to  reach. 
(5)  A  fifth  step  must  frequently  be  taken  by  the 
scientist.  It  may  be  called  the  step  of  verification.  We 

are  not  always  sure  that  the 
conclusion  we  reach  is  the 
exact  truth,  and  we  should 
stand  ready  to  change  our 
views  when  new  facts  or  prin- 
ciples come  to  our  knowledge. 
Many  times  we  may  verify, 
or  prove,  the  truth  of  our 
conclusions  by  further  ques- 
tions or  experiments,  and 
whenever  it  is  possible  this 
should  be  done. 
To  understand  this  method  better,  let  us  now  write 
out  all  that  passed  through  your  mind  as  you  studied 
the  incident  of  the  load  of  wheat.  In  order  to  help  in 
keeping  each  step  separate  from  the  others,  the  second 
one  is  printed  in  ordinary  type ;  the  third  step  —  that 
part  of  the  process  in  which  you  recall  what  you  have 
previously  learned  —  is  inclosed  in  quotation  marks; 
and  the  fourth  step,  or  conclusion,  is  in  heavy-faced  type. 
The  complete  scientific  story  would  run  something  like 
this: 


FIG.  8. 


They  verify  their  con- 
clusion. 


Science  and  the  Scientific  Method  7 

I  see  3  rows  of  bags  with  8  bags  in  each  row  and  there 
is  one  extra  bag  on  top  of  the  others ;  3  times  8  bags  is 
24  bags  and  one  more  makes  25  bags.  "  It  is  probably 
wheat."  "  Each  bag  contains  2  bushels."  There  are 
2  times  25,  or  50,  bushels  in  the  load.  "  A  bushel  of 
wheat  weighs  60  pounds,"  so  the  load  weighs  50  times  60 
pounds,  or  3000  pounds.  "  2000  pounds  make  one  ton," 
hence  there  are  l|  tons  on  the  wagon. 

If  you  had  become  interested  in  this  incident  and  your 
mind  were  active,  perhaps  you  would  not  stop  at  this 
point.  It  is  possible  that  you  would  go  to  the  market 
to  find  whether  this  was  really  a  load  of  wheat  or  not, 
and  what  was  its  exact  weight.  In  this  way  you  would 
verify  your  conclusion  and  thus  carry  out  the  fifth  step 
of  the  process.  You  would,  perhaps,  also  ask  the  farmer 
how  many  acres  of  wheat  he  had  raised  and  how  many 
bushels  per  acre  he  had  secured ;  you  would  learn  what  it 
is  worth  a  bushel  and  compute  the  value  of  the  wheat 
per  acre.  Your  mind  would  perhaps  also  turn  to  the 
number  of  acres  of  wheat  raised  in  the  United  States 
each  year,  the  average  yield  per  acre,  the  total  number 
of  bushels  in  the  crop,  where  the  wheat  will  be  marketed, 
and  the  uses  that  are  made  of  it.  If  you  are  not  inter- 
ested in  such  mental  exercises,  perhaps  you  will  ask 
yourself  why  you  do  not  like  to  think. 

Another  illustration.  Other  illustrations  may  help 
to  give  a  better  understanding  of  the  scientific  method. 
I  see  a  man  on  the  street  clad  in  a  strange  costume  and 
become  interested  in  him.  His  outer  garment,  "  I  can 
hardly  call  it  a  coat,"  is  made  of  that  peculiar  kind  of 


Science  for  Beginners 


FIG.  9. 


cloth  known  as  "  plaid  " ;  I  notice 
that  his  clothing  comes  only  to  his 
knees,  and  that  his  legs  are  bare  from 
the  knee  down  to  the  tops  of  his 
plaid  stockings ;  then,  "  I  remember 
that  such  cloth  and  costume  are  worn 
in  the  northern  part  of  Great  Britain." 
I  conclude  that  he  must  be  a  Scotch- 
man. I  observe  that  he  carries  a 
strange  instrument  and  when  he  puts 
it  to  his  mouth  it  gives  out  an  un- 
usual sound.  "It  is  probably  a 
musical  instrument " ;  it  is  a  pair  of 
bagpipes. 

When  I  return  home,  I  look  up  bagpipes  in  the  diction- 
ary and  find  a  picture  of  a  Scotch  Highlander  with  an 
instrument  like  the  one  I  saw  on  the  street.  I  have 
tested  my  conclusion  and  found  it  correct. 

A  third  illustration.  I  go  fishing ;  presently  I  "get 
a  bite  " ;  I  feel  something  tugging  away  at  my  line. 
It  must  be  a  fish.  I  draw  it  out.  "  What  a  strange 
fish !  "  It  is  long  and  slim  and  slippery ;  it  has  no 
scales.  It  cannot  be  a  common  fish.  I  let  it  touch 
the  ground  and  it  quickly  ties  my  line  into  knots.  "  I 
have  heard  a  fisherman  say  that  eels  do  this."  "I  re- 
member a  picture  of  an  eel  that  I  have  seen."  It  is 
an  eel. 

Still  other  illustrations.  I  am  traveling  on  the 
cars ;  we  pass  through  a  city  in  which  I  see  some  very 
high  buildings.  "  Tall  buildings  are  found  only  in  large 


Science  and  the  Scientific  Method  9 

cities."  This  is  a  large  city.  "  I  remember  that  Grand 
Rapids  is  one  of  the  principal  cities  on  the  railroad 
running  from  my  home  to  Chicago."  This  must  be 
Grand  Rapids.  I  now  consult  my  time  table  to  see 
when  we  are  due  at  the  Grand  Rapids  station  and  find 
that  we  should  be  there  in  two  minutes.  The  brake- 
man  tells  me  that  the  train  is  on  time ;  so  I  am  sure  that 
this  city  is  Grand  Rapids. 

Two  girls  are  expecting  to  go  on  a  picnic.  Early  in 
the  morning  they  scan  the  sky.  Dark,  threatening 
clouds  are  gathering  in  the  east.  "  It  is  going  to  rain  " ; 
we  cannot  go !  They  continue  to  study  the  sky,  and 
presently  the  clouds  break  away  and  the  blue  sky  ap- 
pears. "  It  is  clearing  up  " ;  it  will  not  rain  after  all  and 
we  can  go. 

Two  boys  are  roaming  the  fields  with  their  eyes  wide 
open  to  see  what  they  can  find  that  is  valuable  or  inter- 
esting. They  find  some  bright,  glistening,  yellow  parti- 
cles as  a  part  of  a  rock.  "  It  looks  like  gold.  I  wonder 
if  it  is  gold."  How  shall  we  find  out  whether  it  is  gold? 
"  I've  heard  my  father  say  that  a  mineral  called  fool's 
gold  is  almost  as  bright  and  as  yellow  as  real  gold." 

They  carry  a  piece  of  the  rock  to  their  teacher,  and  he 
takes  them  to  the  chemical  laboratory.  He  tells  them 
that  what  is  called  "  fool's  gold  "  is  not  gold  at  all,  but 
a  compound  of  iron  and  sulfur.  We  can  tell  what  it 
is  by  an  experiment.  If  it  is  pure  gold  it  will  not 
dissolve  in  hydrochloric  acid ;  if  it  is  fool's  gold  it  will 
dissolve  in  the  acid  and  will  give  off  a  disagreeable  odor 
which  will  remind  one  of  decaying  eggs.  Pure  gold  is 


io  Science  for  Beginners 

soft  and  can  be  whittled  with  a  knife.  Fool's  gold  is 
hard  and  generally  separates  from  the  rock  in  small, 
flat  scales.  The  tests  are  made.  The  yellow  mineral 
dissolves  in  the  acid.  It  is  fool's  gold.  By  the  scientific 
method  the  answer  to  the  question  has  been  found. 

Two  additional  advantages  of  the  scientific  method. 
This  is  a  much  better  method  of  getting  knowledge  than 
merely  reading  in  a  book,  because  we  can  understand 
and  use  better  the  knowledge  we  have  worked  out  for 
ourselves,  and  also  because  by  this  method  we  learn  to 
do  our  own  seeing  and  thinking  and  thus  become  able 
to  get  information  that  is  not  to  be  found  in  books.  That 
"  thing  knowledge  is  better  than  book  knowledge  "  you 
will  readily  understand,  and  when  you  remember  that 
the  answers  to  the  problems  that  meet  us  all  through 
life  are  not  written  out  in  books,  you  will  appreciate  the 
importance  of  a  method  that  will  enable  you  to  get  for 
yourself  the  information  you  will  need  in  solving  these 
problems. 

A  clever  scientist.  Near  the  end  of  the  season  a  boy 
announced  the  height  of  a  tall  tree  to  be  33  feet. 

"  Why,  how  do  you  know?  "  he  was  asked. 

"  Measured  it." 

"How?" 

"  Foot  rule  and  yardstick." 

"  You  didn't  climb  that  tall  tree?  "  his  mother  asked 
anxiously. 

"  No'm ;  I  just  found  the  length  of  the  shadow  and 
measured  that." 

"  But  the  length  of  the  shadow  changes." 


Science  and  the  Scientific  Method  n 


FIG.  10.     Measuring  thi  height  of  a  tree. 

"  Yes'm ;  but  twice  a  day  the  shadows  are  just  as 
long  as  the  things  themselves.  I've  been  trying  it  all 
summer.  I  drove  a  stick  into  the  ground,  and  when  its 
shadow  was  just  as  long  as  the  stick,  I  knew  that  the 
shadow  of  the  tree  would  be  just  as  long  as  the  tree,  and 
•that's  33  feet." 


CHAPTER   TWO 

WHAT  THE  YOUNG  SCIENTIST  MUST  LEARN  TO   DO 

THE  scientist  collects  his  facts  or  principles,  arranges 
them  so  that  they  will  give  an  orderly  view  of  the  subject 
as  a  whole,  and  then  draws  his  conclusions  from  them. 
Described  in  this  way  the  method  of  the  scientist  seems 
simple ;  but  in  reality  it  requires  skill  and  care  to  collect 
facts  and  arrange  them  so  that  their  meaning  will  be 
clear.  It  is  very  important,  therefore,  that  the  pupil 
who  is  just  beginning  his  studies  in  science  should  under- 
stand what  he  must  do  to  carry  out  the  scientific  method 
successfully.  This  subject  we  shall  discuss  in  the  present 
chapter,  but  it  should  be  remembered  that  it  is  only  by 
using  the  method  that  a  real  mastery  of  it  will  come  to 
you.  "  Thing  knowledge  is  better  than  book  knowl- 
edge/' whether  it  be  in  baseball,  in  arithmetic,  or  in  the 
method  that  the  scientist  uses  in  his  work. 

The  scientist  must  learn  to  observe.  To  observe 
is  to  take  notice ;  to  see ;  to  give  attention  to  what 
one  sees  and  hears ;  to  perceive ;  to  discover ;  to  learn. 
The  scientist  must  observe  because  it  is  through  obser- 
vation that  he  collects  his  facts.  Have  you  the  ability 
to  observe  accurately?  Can  you  see  clearly  and  can 
you  hear  distinctly?  Are  all  your  senses  wide  awake 
and  on  the  alert?  In  a  word,  are  your  powers  of  ob- 
servation strong  and  active,  and  have  you  formed  the 
habit  of  observation?  A  few  tests  will  help  you  to 
answer  some  of  these  questions. 

Exercise  i.  Let  the  teacher  place  a  few  articles  on  the 
table  and  cover  them  with  a  cloth  or  paper.  Let  the  cover 
be  removed  for  a  minute  and  then  let  each  pupil  make  a  list 


What  the  Young  Scientist  Must  Learn  to  Do    13 

of  the  articles.  What  would  be  your  marking  on  the  scale 
of  a  hundred  in  this  test? 

Exercise  2.  Let  the  teacher  remove  some  of  the  articles 
from  the  table  and  disarrange  the  others.  Then  let  the 
pupils  call  for  the  objects  that  have  been  removed. 

Exercise  3.  If  you  live  in  the  country,  make  from 
memory  a  list  of  the  tools  and  machines  left  without  proper 
shelter  that  you  noticed  on  your  way  to  school  in  the  morn- 
ing. Look  again  when  you  go  home  in  the  evening. 
Let  different  pupils  do  this  and  compare  their  lists. 

Exercise  4.  Make  an  inventory,  from  memory,  of  the 
objects  in  some  room  at  home,  •• —  the  sitting  room,  for 
example.  Take  the  inventory  home  and  find  out  how 
many  prominent  objects  you  have  omitted. 

Exercise  5.  Make  from  memory  a  picture  of  the  face 
of  the  clock  at  home.  What  figure  is  at  the  top?  Which 
is  at  the  bottom?  What  kind  of  figures  are  used?  Do  the 
same  for  your  watch  if  you  have  one.  In  each  case  verify 
your  results. 

The  scientist  must  learn  to  measure.  The  first 
and  most  important  step  in  all  scientific  work  is  to  get 
the  facts  and  get  them  right.  By  the  use  of  rules,  scales, 
and  other  measuring  instruments  we  can  help  our  eyes 
and  ears  and  other  senses  to  make  our  observations 
much  more  exact.  All  our  modern  sciences,  but  espe- 
cially physics,  astronomy,  chemistry,  and  mathematics, 
rest  upon  the  ability  of  the  scientist  to  make  exact 
measurements.  For  linear  measurements  we  use  the 
inch,  the  foot,  the  centimeter,  or  the  meter ;  for  areas, 
the  square  inch,  square  foot,  square  centimeter,  or  square 
meter;  for  cubic  measurements,  the  cubic  inch,  cubic 


14  Science  for  Beginners 

foot,  cubic  centimeter,  or  cubic  meter.  For  measuring 
volume  we  use  the  liquid  pint,  quart,  or  gallon ;  the  dry 
pint,  quart,  or  peck ;  the  liter  and  its  subdivisions  and 
multiples. 

In  the  laboratories  of  our  universities,  scientists  can 
measure  the  size  of  a  disease  germ  that  is  only  one 
fifty-thousandth  of  an  inch  in  diameter ;  they  can  weigh 
the  ink  that  you  use  in  writing  your  name.  Fine  meas- 
urements like  these  are,  of  course,  far  beyond  your 
present  power ;  but  if  you  wish  to  make  true  progress  in 
even  elementary  science,  you  must  become  thoroughly 
acquainted  with  the  units  of  measurement  with  which 
scientists  work.  The  best  way  to  become  acquainted 
with  these  units  is  to  use  them,  and  a  pocket  rule  is  an 
excellent  companion  for  the  knife  that  is  to  be  found  in 
the  pocket  of  almost  every  boy. 


FIG.  ii.     The  best  way  to  become  familiar  with  the  units  of  measurement  is 
to  use  them. 


What  the  Young  Scientist  Must  Learn  to  Do    15 


FIG.  12.     Some  tools  that  a  young  scientist  should  learn  to  use. 

The    young    scientist    must    learn   to    record.      Our 

recollections  of  what  we  have  seen  and  heard  are  too 
scattered  and  unreliable  to  allow  us  to  depend,  in  our 
scientific  work,  on  what  we  remember.  A  third  thing, 
therefore,  that  the  young  scientist  should  learn  to  do  is 
to  keep  a  record.  He  should  be  able  to  use  drawing  in- 
struments well  enough  to  make  a  diagram  or  plan  that 
will  aptly  illustrate  his  thoughts.  He  should  become 
skillful  in  tabulating  his  knowledge,  a  process  which 
will  be  fully  explained  and  illustrated  in  this  book. 

It  is  a  good  plan  always  to  have  at  hand  a  notebook 
into  which  anything  of  importance  may  be  put.  Keep- 
ing this  book  will  afford  many  opportunities  to  practice 
and  develop  the  power  of  recording,  and  it  will  cause 
as  much  mental  gfowth  as  anything  the  pupil  can  do. 

Classification  necessary  in  science.  Science  is  clas- 
sified knowledge,  and  learning  to  classify  is  an  im- 
portant part  of  a  scientific  training.  Let  us  clearly 
understand  what  is  meant  by  .the  term  "  classification," 
and  also  how  a  scientist  must  constantly  use  it  in  order 
to  reduce  his  knowledge  to  a  scientific  form, 


16  Science  for  Beginners 

Two  steps  in  the  process  of  classification.  Classifi- 
cation consists  of  two  separate  steps :  (i)  the  choice  of 
a  proper  basis  for  classification,  and  (2)  the  reference 
of  the  things  to  be  classified  to  that  basis. 

For  example,  suppose  we  should  take  our  stand  at  a 
favorable  place  upon  some  crowded  city  street,  and  make 
a  classification  of  the  people  as  they  pass  by,  and  suppose 
that  we  were  to  take  sex  as  the  basis  of  our  classification. 
This  would  require  us  to  refer  each  person  either  to  the 
class  male,  or  to  the  class  female.  In  most  cases  this 
could  easily  be  done,  but  in  the  case  of  some  foreigners, 
with  their  queer  costumes,  there  might  be  difficulty  in 
making  an  accurate  classification. 

Or  suppose  our  task  were  to  classify  them  as  men, 
women,  boys,  or  girls.  The  difficulties  would  be  some- 
what greater  than  before,  as  it  could  not  always  be  easily 
determined,  in  a  given  case,  whether  a  person  was  really 
a  boy  or  had  passed  the  line  between  boyhood  and  man- 
hood. If  we  were  required  to  classify  them  as  to  height, 
the  problem  would  require  that  every  person  be  halted 
long  enough  to  have  his  measure  taken.  If  the  basis 
of  classification  were  nationality,  and  we  desired  to  do  the 
work  very  accurately,  then  every  person  would  be  re- 
quired to  give  proof  of  the  place  of  his  birth.  Suggest 
several  other  schemes  that  might  be  used  in  classifying 
people  as  they  pass  on  the  street,  and  in  each  case  state 
what  must  be  done  to  carry  out  the  scheme. 

A  wise  basis  of  classification  important.  It  is  very 
important  that  a  correct  basis  of  classification  shall  be 
chosen,  or  else  useless  work  will  be  done.  For  example, 


What  the  Young  Scientist  Must  Learn  to  Do    17 


FIGS.  13  and  14.     The  child  classifies  the  rocks  according  to  their  size;  the 
geologist  according  to  the  materials  of  which  they  are  composed. 


a  librarian  wishes  to  classify  a  collection  of  books  so  that 
they  will  be  most  useful  to  the  readers  who  come  to 
the  library.  He  might  classify  them  according  to  color, 
size,  or  the  material  from  which  the  covers  are  made ; 
but  such  a  classification  would  not  be  well  chosen,  for  it 
is  clear  that  on  any  of  these  bases  books  would  be  thrown 
together  which  are  very  far  apart  in  their  real  character. 
What  would  be  a  better  basis  of  classification?  Why? 
Classification  of  outdoor  objects.  Take  your  stand 
out  of  doors  and  make  a  list  of  20  different  objects  that 
you  see,  such  as  trees,  rocks,  clouds,  houses,  fences,  birds, 
shrubs,  automobiles,  forests,  yards,  and  sidewalks.  You 
will  notice  that  some  of  these  things  have  been  produced 
by  nature,  and  others  have  been  made  by  man.  This  sug- 
gests a  good  basis  of  classification.  Classify  as  natural 
or  artificial  the  objects  you  have  listed. 


1 8  Science  for  Beginners 

Using  the  same  list  of  objects,  notice  that  some  things 
are  alive.  These  things  may  be  classified  as  plants  or 
animals.  What  is  the  difference  between  a  plant  and  an 
animal?  Give  a  good  deal  of  careful  thought  to  this 
question.  What  is  the  difference  between  a  cow  and  a 
cabbage?  How  are  they  alike?  Does  a  cow  require 
food  ?  So  does  a  cabbage.  Does  a  cow  grow  by  means 
of  the  food  it  consumes  ?  So  does  the  cabbage.  Where 
does  the  cow  get  its  food?  Where  does  the  cabbage 
get  its  food  ? 

Exercise  6.  Make  a  list  of  20  animals  that  you  know. 
Make  a  list  of  20  plants  that  you  know.  In  what  ways  do 
the  animals  differ  from  the  plants?  In  what  ways  are  ani- 
mals and  plants  alike  ? 

The  chronological  order.  Sometimes  it  is  best  to 
arrange  facts  or  events  in  what  is  known  as  the  chronolog- 
ical,  or  time,  order;  i.e.,  the  order  in  which  the  events 
occurred  in  time.  For  example,  to  mention  the  names  of 
Washington,  McKinley,  and  Lincoln  would  be  to  arrange 
them  in  a  wrong  order ;  to  speak  of  breakfast,  supper, 
and  dinner  would  be  to  place  the  words  in  a  wrong  order. 
Would  it  be  proper  to  list  them  as  supper,  breakfast, 
and  dinner  ? 

Exercise  7.  Mention  the  days  of  the  week  in  chronologi- 
cal order;  the  months  of  the  year;  the  presidents  of  the 
United  States ;  six  events  which  lead  up  to  a  national  elec- 
tion. Think  of  a  half-dozen  other  lists  of  acts  or  events 
that  can  be  arranged  chronologically. 

The  alphabetical  order.  Another  method  of  arrange- 
ment which  is  frequently  used  by  the  scientist  is  the 


What  the  Young  Scientist  Must  Learn  to  Do    19 

alphabetical  order.  Sometimes  this  is  the  proper  method, 
and  again  it  may  be  unscientific  to  arrange  material  in 
this  way.  If  the  object  is  to  arrange  the  matter  in  such 
a  way  that  any  item  can  be  found  quickly  and  easily, 
the  alphabetical  arrangement  is  the  proper  one.  Thus 
a  book  is  almost  worthless  for  reference  unless  it  has 
an  alphabetical  index;  a  dictionary  that  did  not 
have  this  arrangement  could  not  be  used;  a  list  of 
voters  in  a  township  should  always  be  made  in  this 
way.  *  The  items  on  a  list  which  is  so  made  may  be 
alphabetical  only  as  far  as  their  initial  letters  are  con- 
cerned; but  it  is  better  to  make  the  list  strictly  al- 
phabetical as  to  all  the  letters. 

Exercise  8.  Arrange  alphabetically  the  names  of  the 
pupils  in  your  class ;  the  months  of  the  year ;  the  presidents 
of  the  United  States ;  the  states  of  the  Union ;  the  officers 
of  your  state ;  a  dozen  occupations  followed  by  the  people 
in  your  town.  Make  at  least  six  other  alphabetical  lists. 

Tabulating  facts.  Many  times  the  scientist  finds  that 
the  meaning  of  his  facts  becomes  clearer  and  that  they 
are  more  easily  remembered  if  they  are  tabulated ;  i.e., 
arranged  in  tables.  These  tables  take  whatever  form  the 
scientist  may  choose,  and  it  is  an  excellent  exercise  for  a 
pupil  to  use  his  ingenuity  in  inventing  methods  of  repre- 
senting a  given  series  of  facts.  You  will  have  many 
opportunities  to  do  this  as  you  pursue  the  work  out- 
lined in  this  book. 

Using  the  dictionary.  Most  of  the  thinking  and  re- 
cording of  the  scientist  is  done  in  words,  and  if  his  under- 
standing of  the  meaning  of  words  is  not  exact,  his  thoughts 


20 


Science  for  Beginners 


and  records  cannot  be  accurate  and  clear.  You  should, 
therefore,  very  early  get  into  the  habit  of  taking  your  dic- 
tionary and  looking  up  the  defi- 
nitions of  words,  paying  special 
attention  to  the  meaning  of  the 
Greek  or  Latin  words  from 
which  the  given  word  is  formed. 
Thus  the  word  "  zoology  "  is 
derived  from  two  Greek  words, 
zoon,  meaning  animal,  and  V0#0s, 
a  word  or  discourse,  or  story ; 
hence  zoology  is  the  science 
which  describes  and  classifies 
animals.  The  person  who  is 
well  versed  in  this  science  is 
known  as  a  "  zoologist." 

Exercise  10.  Study  in  the  dic- 
tionary and  enter  in  your  note- 
book the  definitions  of  the  following  sciences:  geography, 
biology,  ornithology,  zoology,  mineralogy,  chemistry,  physics, 
geometry,  trigonometry,  astronomy,  physiology,  history, 
algebra,  chronology. 

What  is  the  meaning  of  the  Latin  verb  from  which  the 
word  "  science  "  is  derived? 

An  exercise  like  the  above  with  the  dictionary,  if  thor- 
oughly done,  is  laboratory  work  just  as  truly  as  is  hand- 
ling any  other  kind  of  apparatus.  To  remind  you  of  the 
importance  of  using  the  dictionary,  certain  words  in  this 
book  have  been  marked  with  a  star  (*) .  To  look  up  these 
and  other  unfamiliar  words  in  the  dictionary  and  to 


FIG.  15.  Using  the  dictionary 
will  help  you  not  only  in  science, 
but  in  all  the  other  intellectual 
work  that  you  do. 


What  the  Young  Scientist  Must  Learn  to  Do    21 

write  them,  with  their  meanings,  in  your  notebook,  will 
help  you  not  only  in  your  science  work,  but  in  all  the 
other  intellectual  work  that  you  do. 

Accuracy  necessary  in  the  scientist.  One  writer 
has  suggested  that  "  talking  about "  a  thing  and  the 
"  science  "  of  the  thing  are  entirely  different.  Talk 
about  a  thing  may  be  random,  scrappy,  fragmentary ; 
much  of  it  may  be  about  things  of  which  the  speaker 
knows  very  little ;  it  may  consist  of  some  statements  he 
is  sure  of  and  of  many  statements  which  are  guesses. 

This  loose  method  is  not  permitted  to  the  scientist. 
He  must  make  his  observations  carefully  and  must  draw 
only  the  conclusions  which  his  facts  will  justify.  Why 
rnust  the  scientist  do  this  ?  Because  the  scientist  is  not 
allowed  to  guess ;  he  must  know.  You,  as  a  young 
scientist,  must  therefore  learn  to  observe  accurately,  in 
order  that  you  may  have  correct  facts  on  which  to  base 
your  conclusions.  You  must  learn  to  weigh  and  measure, 
because  as  long  as  you  do  not  know  whether  an  object 
that  you  are  holding  in  your  hands  is  18  inches  or  a  yard 
long  and  whether  it  weighs  10  pounds  or  20  pounds,  your 
observations  will  be  little  more  than  guesses.  You  must 
learn  to  use  language  with  exactness,  to  keep  a  record  of 
your  observations,  and  to  arrange  your  facts  so  that 
their  meaning  will  be  clear.  '  You  must  draw  only  those 
conclusions  that  are  supported  by  your  facts,  and  if  you 
would  be  a  true  scientist  you  must  avoid  drawing  conclu- 
sions about  subjects  of  which  you  have  no  knowledge. 
Every  single  fact  we  know  of  the  world  about  us  was 
learned  in  this  way. 


CHAPTER  THREE 

MATTER  AND  ITS  FORMS 


FIG.  1 6.     Matter  is  anything  that  occupies  space. 

MUCH  of  the  time  of  a  scientist  is  occupied  with  a 
study  of  matter.  What  is  matter?  Does  the  word 
have  a  definite  meaning  to  you?  Usually  matter  is 
defined  as  "  anything  which  occupies  space  "  or  "  takes 
up  room."  Another  definition  is,  "  Matter  is  anything 
that  has  weight."  It  is  known  to  us  by  means  of  one 
or  more  of  the  senses. 

Matter  distinguished  from  the  immaterial.  Matter 
should  be  distinguished  from  other  things  that  are  not 
matter.  For  example,  a  thought  is  not  matter ;  it  does 
not  occupy  space ;  we  cannot  feel  or  taste  or  see  or  hear 
a  thought.  We  cannot  weigh  a  thought  or  speak  of  its 
size  or  color.  It  is  not  material.  We  say  it  is  im- 
material. 

A  raindrop  is  a  form  of  matter;  it  occupies  space; 
it  has  size,  form,  and  weight.  It  is  material. 

Exercise  i.  Enter  the  names  of  the  following  in  your 
notebook  and  classify  them  as  matter  or  not  matter;  that 

22 


Matter  and  Its  Forms 


is,  as  material  or  immaterial:  a 
snowball;  a  memory;  the  stars  [Hi 
and  stripes;  "Old  Glory "j  ha- 
tred ;  patriotism ;  a  precious  piece 
of  paper  kept  in  Philadelphia 
known  as  the  Declaration  of  In- 
dependence ;  a  man,  meaning  his 
body;  a  man,  meaning  his  char- 
acter; brain;  mind;  the  earth; 
the  sun ;  son ;  tree ;  dream ;  hon- 
esty; iron;  pleasure;  air. 

Three  forms  of  matter.   When 
we  study  matter  and  classify  it 


FIG.  17.  The  flag  itself  is  ma- 
terial; the  sentiments  it  in- 
spires are  immaterial. 


according  to  the  form  it  assumes  under  different  condi- 
tions, —  such  as  a  difference  of  temperature,  —  we  find 
that  it  is  gaseous,  liquid,  or  solid.  Thus,  water  is 
usually  liquid ;  but  if  the  temperature  falls  low  enough 
it  will  become  a  solid,  and  if  the  temperature  is  raised 
high  enough  it  will  take  the  form  of  a  gas.  Air  is 
usually  a  gas,  but  under  conditions  of  extreme  cold 
and  great  pressure  it  assumes  the  liquid  form.  Perhaps 
some  members  of  the  class  have  seen  liquid  air. 

Exercise  2.  Examine  a  piece  of  camphor  gum.  Is  it  a 
solid,  a  liquid,  or  a  gas?  Place  it  in  an  evaporating  dish 
and  gently  heat  it.  What  form  does  it  now  take?  Con- 
tinue the  heating,  taking  care  not  to  burn  the  camphor. 
What  form  does  the  camphor  take  ?  What  becomes  of  the 
camphor?  How  do  you  know  this?  What  form  of  cam- 
phor is  it  that  enters  your  nose? 

Exercise  3.  Name  25  different  forms  of  matter  and  clas- 
sify them  as  gases,  liquids,  or  solids. 


24  Science  for  Beginners 

Exercise  4.  Make  a  list  of  substances  that  may  be  changed 
from  the  solid  to  the  liquid  or  gaseous  form. 

A  definition*  is  a  statement  showing  what  a  word 
means  or  what  a  thing  is.  Can  you  define  a  solid?  a 
liquid?  a  gas?  If  you  cannot,  look  up  these  terms  in 
the  dictionary  or  in  some  book  on  physics  and  enter  the 
definitions  in  your  notebook. 

Division  of  matter.  All  forms  of  matter  may  be  di- 
vided into  very  minute*  particles.  A  stone  may  be 
broken  into  pieces  and  finally  crushed  to  very  fine 
powder;  the  diamond  may  be  reduced  to  dust;  a 
piece  of  ice  may  be  divided  into  particles  so  fine  that 
they  cannot  be  seen;  a  fox  running  through  the 
wood  leaves  enough  odorous  particles  along  his  path- 
way to  enable  the  hound  that  pursues  him  to  keep 
on  his  track. 

Exercise  5.  Dissolve  a  small  amount  of  common  salt 
in  water.  Taste  the  solution.  Is  the  salt  still  there?  Is 
it  visible  to  your  eye?  Can  it  be  recognized  by  your  sense 
of  taste?  Add  more  water  and  continue  to  add  it  as  long 
as  you  can  clearly  distinguish  the  taste  of  the  salt.  Think 
how  very  small  must  be  the  particles 
of  the  salt  that  are  present  in  every 
part  of  the  water. 

Exercise     6.      Dissolve     a     small 
amount  of  dye  in  a  large  vessel  of 
water.      Are    the    particles    of    dye 
present  in  all  parts  of  the  water? 
Exercise  7.   Take  a  round-bottomed 

FIG.  18.    An  evaporating      liter    nask,  —  any    bottle    will    do, - 

dish.  place  in  the  flask  a  small  piece  (one 


Matter  and  Its  Forms 


quarter  as  large  as  a  kernel 
of  wheat)  of  solid  iodin. 
Cork  the  flask.  Hold  it 
over  a  flame  and  heat  it 
very  gently.  Soon  the  solid 
iodin  has  changed  to  a 
beautiful  purple  gas.  The 
particles  of  the  solid  have 
been  driven  far  apart  and 
have  been  separated  from 
each  other,  and  the  gas  now 
occupies  every  portion  of 
the  flask. 

Matter  composed  of  par- 
ticles called  molecules.  An 
experiment*  is  a  question 


FIG.  19.    The  molecules  of  iodin  are 
driven  apart  by  the  heat. 


put  to  Nature.  The  an- 
swers given  back  to  us  are  always  true  and  we  can 
rely  upon  them ;  the  only  difficulty  comes  in  inter- 
preting the  replies.  What  replies  did  we  receive  to 
the  questions  we  have  been  asking  about  matter,  and 
how  shall  we  interpret  them? 

Scientists  interpret  these  experiments  to  mean  that 
matter  is  composed  of  very  small  particles,  —  particles 
so  minute  that  we  cannot  see  them  with  the  most  power- 
ful microscope.  These  small  particles  of  matter  they 
call  molecules.  Thus  they  speak  of  the  molecules  of 
water,  of  gold,  or  of  salt. 

The  smallest  particle  into  which  matter  can  be 
divided  without  changing  its  nature  is  called  a 
molecule. 


26  Science  for  Beginners 


FIG.  20.     In  a  solid  the  molecules  are  confined  in  their  places;    in  a  liquid 
they  hold  together  but  move  easily  over  each  other;  in  a  gas  they  fly  apart. 

A  group  of  molecules  make  a  mass  of  matter. 

The  difference  between  solids,  liquids,  and  gases. 
Turn  now  to  your  notebook  and  read  the  definitions 
you  have  written  of  a  solid,  a  liquid,  and  a  gas.  What 
is  the  difference  in  the  condition  of  the  molecules  in 
these  three  states  of  matter?  If  you  think  over  this 
question  carefully,  you  will  come  to  the  following  con- 
clusions : 

(1)  In  a  solid  the  molecules  are  held  firmly  together 
and  are  confined  quite  closely  to  their  places.     They 
cannot  move  about  to  any  great  extent  or  slide  on  each 
other.     A  solid,  therefore,  keeps  the  same  form. 

(2)  In  a  liquid  the  molecules  hold  together  less  firmly, 
and  they  can  slip  easily  over  each  other.     For  this  reason, 
liquids  flow  about  and  are  able  to  take  any  shape.     A 
liquid  will  always  take  the  shape  of  the  vessel  into 
which  it  is  placed,  except  that  the  top  remains  flat. 

(3)  In  a  gas  the  molecules  are  entirely  separate  and 
instead  of  holding  together  fly  apart  as  widely  as  possible. 
The  walls  of  a  blown-up  football  are. kept  pushed  out- 
ward by  the  ceaseless  hammering  of  millions  of  air  mole- 


Matter  and  Its  Forms  27 

cules  that  beat  against  them,  and  the  pressure  in  a  boiler 
is  caused  by  the  steam  molecules  striking  against  its 
sides. 

Study  again  the  experiments  you  have  performed 
and  explain  what  the  molecules  do  in  each  one.  Can 
you  think  of  any  substances  that  are  midway  between  a 
solid  and  a  liquid  in  their  nature  ? 

A  closing  thought.  We  will  close  this  lesson  by  re- 
calling the  idea  that  everything  in  this  world  is  either 
material  or  immaterial,  and  that  matter  is  composed  of 
an  infinite  number  of  little  parts,  called  molecules.  In 
a  stone  the  molecules  are  prisoners  chained  to  their 
places;  in  a  brook  they  are  an  army,  sliding  and  roll- 
ing over  each  other  on  their  way  to  the  sea ;  in  the  air 
they  are  a  multitude  of  tiny  particles,  dancing  and  shoot- 
ing about.  Matter  is  a  wonderful  thing,  and  many 
interesting  experiments  can  be  done  with  it. 


CHAPTER  FOUR 

SOME  PROPERTIES  OF  MATTER 


FIG.  21.     "I  am  the  daughter  of  Earth  and  Water, 
And  the  nurseling  of  the  sky ; 
I  pass  thro'  the  pores  of  ocean  and  shores ; 
I  change,  but  I  cannot  die."  —  SHELLEY  :   The  Cloud. 

IN  the  last  chapter  we  learned  that  matter  is  any- 
thing that  occupies  space.  This  definition  tells  us  what 
matter  is,  but  it  does  not  tell  us  what  it  is  like  or  what 
we  can  do  with  it.  Since  the  scientist  spends  much 
of  his  time  working  with  matter,  we  shall  in  this  chapter 
investigate  some  of  its  properties.  This  is  only  another 
way  of  saying  that  we  shall  try  to  find  out  what  we  can 
and  what  we  cannot  do  with  it. 

Impenetrability  of  matter.  Impenetrability*  is  a 
property  of  all  matter.  Exactly  what  is  meant  by  the 
term  "  impenetrability  "  will  be  made  clear  by  a  few 
experiments : 

Exercise  i.  Have  a  boy  stand  upon  the  floor  and  with 
a  piece  of  crayon  draw  a  circle  just  inclosing  his  feet.  Now 
let  a  second  boy  try  to  occupy  this  circle  with  the  first  one. 
Can  two  boys  occupy  the  same  space  at  the  same  time  ? 

28 


Some  Properties  of  Matter 


29 


This  may  seem  to  be  a  foolish  question,  and  you  will 
say,  "  Of  course  two  boys  cannot  occupy  the  same 
space  at  the  same  time."  That  is  true,  but  let  us  see 
if  you  are  as  ready  to  make  this  assertion  about  some 
things  besides  boys. 

Exercise  2.  Take  a  tumbler  and  a  dish  of  water.  Hold 
the  tumbler  bottom  up  and  press  its  mouth  down  deep 
into  the  water.  What  is  in  the  tumbler  when  it  is  first  placed 
in  the  water  ?  Does  the  water  rise  and  fill  the  glass  ?  Why  ? 

The  answer  is  the  same  as  before.  The  air  and  the 
water  cannot  occupy  the  same  space  at  the  same  time. 

Exercise  3.     Tip  the  tumbler  to  one  side  while  still  press- 
ing down  upon  it.     What  happens?    Be  sure  to  notice  that 
two      things        happen. 
Which  happens  first  ? 

Exercise  4.  Stand  a 
good-sized  bottle  or  jug 
upright,  and  pour  water 
into  it  rapidly.  What 
happens  ?  Why  ?  When 
the  jug  is  full  of  water, 
turn  it  over  with  the 
mouth  down.  What 
two  things  happen  ? 
Which  happens  first? 

Exercise  5.  Drive  a 
nail  into  a  pine  board. 
Do  the  nail  and  the 
wood  occupy  the  same 
space  at  the  same  time, 

or  does  the  nail  push  aside      FlG  22    why  does  not  the  water  enter 
the  wood  in  order  to  make  the  bottle  ? 


Science  for  Beginners 


FIG.  23.     The  nail   and   the  wood  cannot 
occupy  the  same  space  at  the  same  time. 


a  place  for  itself?  Draw 
out  the  nail  and  see  if  the 
wood  has  been  pushed 
aside.  Try  the  same  ex- 
periment in  water.  Ac- 
count for  the  difference  in 
results. 

Thus  you  find  it  is  true 
that   no  two  bodies    or 


substances  can  occupy  the  same  space  at  the  same  time. 
This  fact  is  true  of  all  forms  of  matter,  and  this  property 
or  quality  of  matter  is  known  as  impenetrability. 

Exercise  6.  Raise  a  window  about  three  inches  at  the 
bottom  and  with  a  smoke  paper 1  see  whether  the  air  is 
passing  out  of  the  room.  Do  you  see  why  opening  a  win- 
dow oftentimes  fails  to  accomplish  its  purpose  ?  Could  pure 
air  enter  the  room  until  some  of  the  air  already  in  the  room 
had  passed  out?  Lower  the  window  from  the  top  without 
closing  the  opening  at  the  bottom,  and  test  the  flow  of  the 
air  at  both  places.  Two  openings  are  better  than  one  if 
we  wish  to  get  fresh  air  into  a  room. 

Exercise  7.  Take  a  tall,  slim  bottle  or  tumbler  and  fill 
it  partly  full  of  water.  Mark  the  top  of  the  water  very 
accurately  by  pasting  a  strip  of  paper  even  with  it.  Then 
slowly  add  salt  or  sugar,  allowing  it  to  dissolve  in  the  water. 
Can  you  add  a  considerable  amount  of  salt  without  caus- 
ing the  water  to  rise  above  the  mark? 

1  A  good  smoke  paper  may  be  had  by  rolling  a  piece  of  brown  wrapping 
paper  into  a  compact  roll.  This  is  lighted,  and  when  burning  freely  the 
flame  is  extinguished.  A  piece  of  filter  paper  or  other  soft  paper  soaked 
in  a  solution  of  potassium  nitrate  makes  an  excellent  smoke  paper. 


Some  Properties  of  Matter  31 

In  this  case  the  salt  and  the  water  seem  to  occupy  the 
same  space  at  the  same  time;  but,  suppose  you  had  a 
bushel  basket  full  of  apples,  could  you  not  still  add  a 
large  number  of  marbles  without  filling  the  basket  more 
than  full  ?  So  the  case  of  the  sugar  dissolved  in  water  is 
explained  by  saying  that  there  are  spaces  between  mole- 
cules and  that  the  molecules  of  the  sugar  occupy  the 
spaces  between  the  molecules  of  the  water.  Two  mole- 
cules cannot  be  in  the  same  place  at  the  same  time  any 
more  than  two  boys  or  two  marbles  can  be  in  the  same 
place  at  the  same  time. 

Malleability.  Impenetrability  is  a  property  of  all 
matter,  but  certain  other  properties  may  be  possessed  by 
some  substances  and  not  by  others.  Such  a  property 
is  malleability.*  Perform  the  following  experiment 
and  you  will  understand  the  meaning  of  the  term : 

Exercise  8.  Place  a  piece  of  lead  on  some  flat,  hard 
surface,  as  an  anvil,  and  hammer  it.  It  spreads  out  under 
the  hammer  without  being  broken.  It  is  evident  that  the 
molecules  of  the  lead  change  their  relative  positions  during 
this  process.  Under  the  force  exerted  on  them  by  the  blows 
of  the  hammer  they  slip  on  each  other  to  some  extent. 

Metals  are  extensively  used  in  industry,*  and  one 
great  advantage  that  many  of  them  have  over  wood 
and  stone  is  that  they  are  malleable.*  Of  all  the  metals 
platinum  and  gold  are  the  most  malleable ;  gold  can  be 
rolled  into  leaves  so  thin  that  it  would  take  300,000  of 
them  to  make  the  thickness  of  one  inch.  Tin  also  can 
be  rolled  quite  thin,  as  you  may  see  for  yourself  by  ex- 


32  Science  for  Beginners 

amining  a  piece  of  tin  foil.  Iron  is  quite  malleable  when 
heated,  and  thousands  of  men  work  in  great  mills,  roll- 
ing it  into  rails,  girders  for  buildings  and  bridges,  sheets 
for  roofs  and  tanks,  and  dozens  of  other  forms.  Copper 
is  more  malleable  at  ordinary  temperature  than  when 
it  is  heated. 

Exercise  9.  Test  various  substances  as  to  malleability: 
a  pin,  a  nail,  a  penny,  a  nickel,  shot,  a  pebble,  a  piece  of 
cold  glass.  Record  the  results  of  these  tests  in  your  note- 
book. 

Ductility.  When  a  solid  can  be  drawn  out  into  a 
fine  thread  or  wire,  it  is  said  to  be  ductile,*  and  this 
property  of  a  solid  is  known  as  ductility.  Iron,  copper, 
and  many  other  metals  are  ductile. 

Exercise  10.  Heat  a  piece  of  glass  tubing  until  it  is  soft 
and  flexible.  Then  draw  the  ends  of  the  tubing  away  from 
each  other;  the  heated  part  will  be  drawn  out  into  thin 
threads.  To  prove  that  these  threads  are  still  tubes,  place 
one  end  in  colored  water  or  ink,  and  notice  that  the  liquid 
rises  inside. 

Platinum  and  gold  can  be  drawn  into  wires  as  fine 
as  a  spider's  web,  —  wires  so  small  that  they  can  scarcely 
be  seen  without  a  magnifying  glass.  It  is  a  remarkable 
fact  that  the  strength  of  some  metals  is  increased  by 
drawing  them  out  into  wires,  and  for  this  reason  a  drawn 
wire  is  stronger  than  an  ordinary  piece  of  the  metal  of 
the  same  thickness.  Cables  made  by  twisting  iron 
wires  together  will  support  a  much  greater  weight  than 
solid  iron  rods  of  the  same  size,  and  such  cables  are  used 
in  the  building  of  suspension  bridges  where  great  strength 


Some  Properties  of  Matter  33 


FIG.  24.    After  glass  has  been  heated,  it  can  be  drawn  out  into  fine  threads. 

is  required.  The  great  Suspension  Bridge  at  Niagara 
Falls  is  an  example  of  a  bridge  of  this  kind. 

Brittleaess.  Substances  that  are  not  malleable  or 
ductile  will  crumble  into  small  pieces  when  struck  with 
a  hammer.  Examples  of  such  substances  are  cold 
glass,  almost  all  rocks,  ivory,  chalk,  ice,  an  eggshell. 
This  property  is  called  brittleness,  and  substances  pos- 
sessing it  are  said  to  be  brittle.  Find  other  examples 
of  brittle  substances. 

Elasticity.  Certain  substances  return  to  their  original 
form  when  this  has  been  changed  by  some  force  applied 
to  them.  By  this  return  to  the  original  form  the  mole- 
cules come  back  to  the  places  they  occupied  before  the 
change.  This  property  is  called  elasticity,  and  sub- 
stances possessing  it  are  said  to  be  elastic. 

Exercise  n.  Stretch  a  rubber  band  or  compress  a  rubber 
ball  and  watch  it  return  to  its  original  form.  Test  various 
articles  as  to  elasticity:  wood,  ivory,  gum,  whalebone, 
copper,  iron,  lead,  steel,  a  drawn:out  glass  tube  or  a  thin 


34  Science  for  Beginners 

sheet  of  glass.  Bend  each  one  and  notice  what  happens 
when  the  force  is  removed. 

What  happens  when  moist  snow  is  pressed  between 
the  hands?  when  a  rubber  ball  is  thrown  against  the 
sidewalk  ? 

Flexibility.  Elasticity  is  to  be  carefully  distinguished 
from  another  property  which  a  substance  shows  when 
it  bends  but  fails  to  return  to  its  original  form  or  size. 
In  this  latter  case  the  substance  is  said  to  be  flexible,* 
or  to  possess  the  property  of  flexibility.  Is  a  cord 
elastic  ?  Is  it  flexible  ?  Which  of  the  substances  tested 
in  Exercise  1 1  are  flexible  ? 

Hardness.     One  solid  is  said  to  be  harder  than  another 

**•*• 

when  it  will  scratch  or  make  a  mark  upon  the  other 
substance.  The  diamond  will  scratch  glass  because  it 
is  harder  than  glass ;  a  knife  blade  will  scratch  a  piece 
of  limestone  because  it  is  harder  than  limestone ;  the 
knife  blade  will  not  scratch  a  piece  of  quartz,  because  it 
is  softer  than  the  quartz. 

Why  does  the  ax  cut  the  wood  instead  of  the  wood 
cutting  the  ax  ?  Is  a  file  or  a  saw  made  of  harder  mate- 
rial? State  some  of  the  disadvantages  man  would  be 
under  if  all  solids  possessed  the  property  of  hardness  in 
equal  degree. 

Indestructibility.  Matter  cannot  be  destroyed;  we 
may  change  its  form  or  even  make  it  invisible,  but  all 
matter  possesses  the  property  of  indestructibility. 

Exercise  12.  Into  a  tin  cup  —  or  better,  an  evaporating 
dish  —  containing  water,  place  a  small  amount  of  sugar.1 
1  Copper  sulfate  may  be  used  instead  of  sugar. 


Some  Properties  of  Matter 


35 


FIG.  25.     A  condenser  of  the  kind  that  chemists  use  in  their  laboratories. 
Explain  how  it  works  and  for  what  purpose  it  is  used. 

The  sugar  disappears  from  sight.  Has  it  been  destroyed? 
Taste  the  solution  and  notice  that  it  has  the  well-known 
sweet  taste  of  sugar. 

Place  the  dish  on  the  stove  or  over  a  flame  and  with  gentle 
heat  boil  away  the  water  until  the  sugar  is  dry.  Do  not  let 
the  sugar  burn.  Now  taste  the  solid  and  convince  yourself 
that  you  have  the  sugar  back  again. 

In  the  experiment  just  made,  it  might  seem  that  the 
water  had  been  destroyed.  It  certainly  became  in- 
visible and  disappeared.  Was  it  destroyed?  By  hold- 
ing a  cold  glass  over  the  dish  you  can  prove  that  the 
water  is  escaping  as  a  gas  into  the  air,  and  if  a  distilling 
apparatus  is  at  hand,  all  the  water  which  escapes  in  the 
form  of  steam  may  be  condensed  and  recovered. 

The  law  of  the  conservation  of  matter.  Thus  it  is 
true  for  all  kinds  of  matter  that  we  may  change  its 
form  but  we  cannot  destroy  it.  We  may  put  a  stick  of 


36  Science  for  Beginners 

wood  into  the  fire  and  it  is  wonderfully  changed,  but  the 
identical  matter  that  formerly  existed  in  the  wood  either 
remains  in  the  ashes  or  goes  up  the  chimney  in  smoke 
or  invisible  gas.  Matter  can  be  neither  created  nor 
destroyed.  In  the  universe  there  exists  today  exactly 
the  same  amount  of  matter  that  existed  in  it  millions 
of  years  ago.  This  is  known  as  the  great  Law  of  the 
Conservation*  of  Matter. 


CHAPTER   FIVE 


CHANGES  IN  MATTER 


FIG.  26.  After  wax  is  melted  it  is  still 
wax ;  the  change  in  it  is  a  physical  change, 
and  its  identity  is  not  destroyed. 


THE  observant  per- 
son is  impressed  by  the 
fact  that  changes  are 
going  on  all  about  him. 
The  wood  that  is  placed 
in  the  stove  is  changed 
into  the  gases  that  go 
up  the  chimney  and 
the  ashes  that  remain 
in  the  stove.  The  sour 
milk  and  the  soda  that 
are  used  in  the  making 
of  griddle  cakes  has 
each  its  own  peculiar 

taste,  but  in  the  cooking  process  these  two  substances 
evidently  are  changed,  for  we  do  not  detect*  either  when 
we  eat  the  cakes.  A  bright  knife  blade  which  is  care- 
lessly left  in  moist  air  changes  to  a  brown,  crumbling  sub- 
stance that  we  call  "rust."  The  materials  that  a  tree 
draws  from  the  earth  are  changed  into  flowers  or  fruits, 
and  the  food  that  a  bird  or  a  sheep  eats  becomes  feathers 
or  wool.  Matter  cannot  be  destroyed,  but  great  changes 
in  matter  can  easily  be  brought  about. 

Two  kinds  of  changes  in  matter.  Sometimes  a 
change  in  matter  is  only  temporary*  and  the  substance 
can  be  made  to  return  to  its  former  condition,  as  when 
ice  is  formed  from  water,  or  steam  from  water,  or  water 
from  steam.  Other  examples  of  this  kind  of  change  are 

37 


Science  for  Beginners 


FIG.  27.  ,But  after  wax  has  been  burned 
it  is  no  longer  wax;  it  has  undergone  a 
chemical  change  and  its  identity  is  lost. 


seen  in :  a  piece  of  iron 
which  has  been  heated 
and  then  cooled ;  a  piece 
of  wood  that  is  bent 
and  then  allowed  to 
straighten  out ;  a  piece 
of  wax  that  is  melted 
and  then  hardens ;  a 
piece  of  iron  which  is 
attracted  by  a  magnet 
and  then  has  the  power 
to  attract  other  pieces 
of  iron.  In  these  cases 
the  substances  have  not 
lost  those  qualities  by  which  we  describe  or  identify  them. 
After  being  heated  iron  is  still  iron,  after  being  bent  wood 
is  still  wood,  and  after  being  melted  wax  is  still  wax. 

Changes  of  this  kind  are  known  as  physical  changes. 
All  such  changes  are  studied  in  the  science  known  as 
physics. 

Sometimes  permanent*  changes  take  place  in  matter 
and  the  substances  never  return  to  their  former  condi- 
tion, as  when  iron  rusts  or  a  piece  of  wood  decays. 
Other  examples  of  such  changes  are :  the  decay  of  fruits 
and  vegetables ;  the  souring  of  milk ;  cider  changing  into 
vinegar ;  the  digestion  of  food ;  the  burning  of  wood 
or  coal.  In  all  such  cases  the  substances  have  lost  their 
former  qualities  and  have  taken  on  new  ones ;  they  have 
been  broken  up  and  new  substances  have  been  formed 
from  them.  Such  alterations*  or  changes  are  called 


Changes  in  Matter  39 

chemical  changes,  and  they  are  studied  in  the  science 
known  as  chemistry.  In  practical  life  physics  and  chem- 
istry are  closely  related;  the  engineer  sets  going  a 
chemical  process  when  he  throws  coal  into  the  fire  and 
a  physical  process  when  he  turns  on  the  steam. 

Exercise  i.  Take  a  third  of  a  test  tubeful  of  granulated 
sugar.  Notice  that  the  sugar  is  a  white  solid  and  that  it 
has  its  own  peculiar  taste.  Heat  it  gradually  by  placing 
the  test  tube  in  or  near  the  flame  of  an  alcohol  lamp  or 
Bunsen  burner.  It  changes  color  and  dissolves.  Presently 
it  becomes  black.  Taste  it.  A  change  has  taken  place. 
Charcoal,  or  carbon,  has  been  produced.  What  kind  of 
change  have  we  in  this  case  ? 

Atoms.  How  shall  we  explain  what  has  happened 
in  the  test  tube?  A  chemical  change  has  taken  place, 
and  the  chemist  explains  it  by  supposing  that  molecules 
are  made  of  still  smaller  particles  which  are  called 
atoms,  and  that  when  the  sugar  is  heated  the  molecules 
are  broken  up  and  new  substances  are  built  from  the 
atoms  that  were  in  them.  One  of  these  new  substances 
is  the  carbon  that  remains  in  the  test  tube. 

An  atom  is  the  smallest  particle  into  which  matter  is 
divided  in  chemical  changes. 

A  molecule  is  made  up  of  two  or  more  atoms.  Would 
it  be  correct  to  speak  of  an  atom  of  sugar? 

Chemistry  is  the  science  of  the  atom  and  of  how  atoms 
combine  with  each  other  to  form  molecules. 

Exercise  2.  Take  two  tumblers  or  beaker  glasses  of  the 
same  size.  Set  them  on  a  table  at  least  a  yard  apart.  Rinse 
one  with  ammonium  hydroxid  and  the  other  with  hydro- 


Science  for  Beginners 


chloric  acid.  Cover  one  with  a 
paper  and  bring  it  to  the  mouth 
of  the  other.  Withdraw  the 
paper.  What  takes  place? 

The  scientist  believes  that 
the  molecules  of  these  two 
gases  have  •  been  broken  up 
and  the  atoms  in  them  used 
to  build  the  white  solid  (am- 
monium chlorid)  that  has 
been  formed. 

Exercise  3 .  Chew  thoroughly 
some  kernels  of  wheat  (puffed 
wheat  will  do)  and  hold  them 
in  the  mouth  for  some  time. 
Observe  carefully.  Do  you  de- 
tect, after  a  while,  a  sweet 
taste? 

The  explanation  is  that  the  saliva  has  changed  the 
starch  in  the  wheat  to  sugar.  The  starch  molecules 
have  been  broken  up  and  sugar  molecules  have  been 
formed. 

Exercise  4.  With  a  pair  of  forceps  hold  a  piece  of  mag- 
nesium ribbon  in  a  flame.  What  takes  place  ? 

The  ribbon  burns,  and  in  the  process  the  silvery  and 
malleable  metal,  magnesium,  is  changed  to  a  white  and 
very  brittle  substance  known  as  magnesium  oxid. 
What  kind  of  change  is  this? 

Elements.  Many  substances  can  be  broken  up  into 
simpler  ones,  but  there  are  some  substances  that  cannot 


FIG.  28.  The  molecules  of  the 
two  invisible  gases  are  broken  up, 
and  the  atoms  in  them  are  used  to 
build  a  white  solid. 


Changes  in  Matter  41 

be  so  divided.  For  example,  the  chemist  cannot  get 
from  a  piece  of  pure  gold  anything  but  gold,  or  from 
pure  silver  anything  but  silver.  The  atoms  in  the  mole- 
cules of  gold  and  silver  are  all  alike,  and  it  is  impossible 
to  divide  the  molecules  into  substances  of  different  kinds. 
A  substance  that  has  in  it  only  one  kind  of  atom  is  called 
an  elementary  substance,  or  an  element.  On  page  371 
a  table  of  some  of  the  more  common  elements  is  given. 
About  85  elements  are  now  known. 

Compounds.  When  the  molecules  of  a  substance  are 
composed  of  two  or-  more  atoms  that  are  different  from 
each  other,  we  have  a  compound  substance,  or  a  com- 
pound. If  we  pass  electricity  through  water,1  we  find 
that  the  water  decomposes*  into  two  substances,  oxygen 
and  hydrogen,  and  we  therefore  say  that  water  is  not 
an  element  but  a  compound  of  hydrogen  and  oxygen. 

The  number  of  elementary  substances  in  the  world 
is  very  small  as  compared  to  the  number  of  compounds. 
When  we  decompose  and  study  the  thousands  of  known 
compounds,  we  find  only  85  different  kinds  of  atoms 
in  them  all.  Many  of  the  elements  are  so  rare  as  to 
be  of  only  passing  interest  to  the  practical  man.  Hence 
the  ordinary  course  in  chemistry  includes  the  study  of 
only  about  35  elements  and  the  compounds  which  are 
formed  from  them. 

Chemical  symbols.  Chemists  have  devised  a  system 
of  shorthand  writing  by  which  they  use  brief  symbols 
for  the  elements  instead  of  writing  out  the  full  names. 
Generally  the  symbol  is  an  abbreviation  of  the  English 

1 A  little  sulfuric  acid  is  added  to  the  water  to  conduct  the  electricity. 


4#  Science  for  Beginners 

or  Latin  name  of  the  element.  For  example,  the  symbol 
for  oxygen  is  O ;  for  carbon,  C ;  for  calcium,  Ca ;  for 
iron,  Fe  (Latin,  ferrum) ;  and  for  gold,  Au  (Latin, 
aurum) . 

Chemical  formulas.  Chemists  have  also  a  brief  and 
simple  way  of  indicating  the  elements  and  the  number 
of  atoms  in  chemical  compounds.  They  write  one 
after  another  the  symbols  of  the  elements  in  the  mole- 
cule of  the  compound ;  and  with  small  subscript*  figures 
they  show  the  number  of  each  kind  of  atoms.  Thus 
H20  (read  this  formula  "  H-two-O ")  stands  for  i 
molecule  of  water,  which  contains  3  atoms,  —  2  of 
hydrogen  and  i  of  oxygen.  H2SO4  (H-two-S-O- 
four)  stands  for  i  molecule  of  sulfuric  acid,  containing 
7  atoms,  —  2  of  hydrogen,  i  of  sulfur,  and  4  of  oxygen. 
Ci2H22On  (C-twelve-H-twenty-two-O-eleven)  stands 
for  a  molecule  of  common  sugar  with  45  atoms,  — 12 
atoms  of  carbon,  22  of  hydrogen,  and  n  of  oxygen. 
In  a  similar  way  the  composition  of  all  chemical  com- 
pounds may  be  represented  by  chemical  formulas. 

Some  facts  to  remember.  Matter  undergoes  physical 
and  chemical  changes.  In  physical  changes  the  identity 
of  the  substances  is  not  destroyed;  the  molecules  are 
not  broken  up  and  the  substances  can  return  to  their 
original  form.  In  chemical  changes  the  identity  of 
the  substances  is  lost ;  they  are  decomposed  and  from  the 
materials  of  which  they  were  composed  new  and  different 
substances  are  formed.  Tn  such  changes  the  molecules 
of  the  substance  are  broken  to  pieces  and  the  atoms  in 
them  are  used  to  build  new  and  different  molecules. 


Changes  in  Matter  43 

All  cases  of  chemical  change  follow  the  law  of  the 
conservation  of  matter.  When  the  molecules  are  broken 
up,  the  atoms  in  them  are  not  destroyed ;  they  are  only 
separated  from  each  other,  and  they  at  once  unite  with 
other  atoms  to  form  new  substances.  Every  atom  that 
was  in  the  original  substances  will  be  found  in  the  new 
substances  that  are  formed. 


CHAPTER   SIX 

OXYGEN:   THE  ACTIVE  ELEMENT 


FIG.  29.    By  weight,  oxygen  constitutes  one  half  of  the  earth's  crust,  eight 
ninths  of  water,  and  about  one  fifth  of  the  atmosphere. 

OXYGEN  is  by  far  the  most  abundant  of  the  elements. 
By  weight,  it  constitutes  one  half  of  the  crust  of  the 
earth,  eight  ninths  of  water,  and  about  one  fifth 
of  the  atmosphere.  Not  only  is  oxygen  the  most  abun- 
dant element,  but  it  is  also  the  most  active  in  forming 
compounds;  its  atoms  unite  with  the  atoms  of  other 
elements  to  form  substances  of  many  different  kinds. 
It  also  enters  into  the  composition  of  nearly  all  the 
substances  to  be  found  in  plants  and  animals.  This 
latter  fact  will  be  more  thoroughly  studied  in  a  later 
chapter. 

Preparing  oxygen.  Oxygen  may  be  obtained  by  heat- 
ing potassium  chlorate  or  manganese  dioxid  or,  better 
still,  a  mixture  of  the  two.  Both  these  substances 
contain  oxygen,  and  when  they  are  heated  their  mole- 

44 


Oxygen :    the  Active  Element  45 

cules  are  broken  up  and  the  oxygen  in  them  is  set  free. 
The  process  is  as  follows : 

Exercise  i.  Powder  a  small  quantity  of  pure  potassium 
chlorate  and  mix  it  with  one  fourth  as  much  manganese 
dioxid  (black  oxid  of  manganese).  Keep  the  mixture  per- 
fectly dry  and  free  from  dust  or  other  foreign  matter.  Fill 
an  ignition  tube  about  one  third  full  of  the  mixture.1  Close 
the  tube  with  a  cork  through  which  passes  a  small  delivery 
tube  (Fig.  30).  Support  the  tube  in  a  slanting  position  and 
apply  heat.  Heat  the  upper  part  of  the  mixture  first  and 
regulate  the  heat  so  that  the  gas  will  be  given  off  at"  a  uniform* 
rate.  The  gas  can  be  collected  in  bottles  filled  with  water 
and  inverted  in  a  vessel  of  water  (Fig.  38).  Fill  several 
bottles  with  the  gas.  Close  the  bottles  with  a  glass  plate 
or  cork  and  stand  them  upright.  Keep  them  stoppered  or 
covered.  Why  ?  Remove  the  delivery  tube  from  the  water 
before  the  lamp  is  taken  away  from  under  the  test  tube. 

Oxygen  is  a  transparent,*  colorless,  tasteless,  odorless 
gas.  If  you  remember  that  the  air  you  have  been 
using  all  your  life  contains  oxygen,  you  will  know  that 
the  last  four  statements  are  true. 

Exercise  2.  Light  a  pine  stick  and  let  it  burn  until  a 
bright  coal  of  fire  will  remain  when  the  flame  is  blown  out. 
Thrust  the  glowing  stick  into  one  of  the  bottles  of  oxygen. 
Notice  that  the  gas  itself  does  not  burn,  but  the  stick  imme- 
diately bursts  into  a  very  bright  flame. 

1  An  ignition  tube  is  made  of  hard  annealed  glass,  which  will  not 
melt  or  crack  except  under  very  intense  heat.  An  ordinary  test  tube 
may  be  used  in  this  experiment  if  care  is  taken  in  heating  it.  A  copper 
or  iron  retort  may  be  used  to  advantage  when  a  large  amount  of  oxygen 
is  desired. 


Science  for  Beginners 


FIG.  30.    Preparing  oxygen  from  one  of  its  compounds. 

Two  things  are  to  be  noticed:  first,  the  gas  itself 
does  not  burn ;  secondly,  it  causes  the  stick  to  burn,  or, 
as  the  chemist  would  say,  it  supports  combustion. 

Exercise  3.  Fasten  a  piece  of  charcoal  —  a  piece  made 
from  bark  is  best  —  to  a  wire  and,  after  it  has  been  ignited, 
lower  it  into  a  jar  of  oxygen.  Brilliant  combustion  will 
take  place  and  will  continue  until  all  of  either  the  oxygen  or 
the  bark  is  consumed  (Fig.  31). 

After  trying  the  above  experiment,  ask  yourself 
two  or  three  questions :  What  did  you  put  into  the 
bottle?  Remember  that  both  charcoal  (or  carbon, 
which  is  another  name  for  it)  and  oxygen  are  elements. 
What  do  the  atoms  of  oxygen  and  carbon  do  when  the 
charcoal  burns?  What  does  the  bottle  contain  at  the 
close  of  the  experiment?  Evidently  it  must  be  a  com- 


Oxygen :   the  Active  Element 


47 


FIG.  31.     Charcoal  burning  in  a  bottle  of  oxygen. 

pound  of  carbon  and  oxygen.  -•  It  is,  in  fact,  the  well- 
known  gas  called  carbon  dioxid. 

C  +  O2      ->        CO2 

carbon  +  oxygen  produces  carbon  dioxid 

Exercise  4.  Take  a  short  piece  of  crayon  and  with  a 
knife  cut  out  a  small  cup.  Attach  the  cup  to  a  wire  and 
you  have  a  deflagrating*  spoon.  Load  it  with  sulfur, 
ignite  the  sulfur,  and  lower  it  into  a  jar  of  oxygen.  Hold 
it  until  the  sulfur  is  all  consumed.  What  was  in  the  jar 
at  the  beginning?  What  did  you  put  into  it?  What  is 
in  the  jar  at  the  close  of  the  experiment?  Cautiously  smell 
the  gas  in  the  jar  and  compare  it  with  the  odor  obtained  from 
burning  sulfur.  The  two  gases  are  identical.* 

You  have  added  a  solid  to  a  gas  and  obtained  another  gas. 

S  +  O2      ->         SO2 

sulfur  +  oxygen  produces  sulfur  dioxid 


Science  for  Beginners 


FIG.  32.    Even  iron  will  burn  in  a  jar  of  oxygen. 

Exercise  5.  Take  a  piece  of  iron  picture-wire.1  It  should 
be  long  enough  to  reach  to  the  bottom  of  the  jar  contain- 
ing oxygen.  Heat  one  end  of  it  by  placing  it  in  a  flame 
for  an  instant,  and  then  dip  it  into  some  sulfur.  The  sulfur 
will  adhere  to  the  iron  and  by  burning  will  raise  the  tem- 
perature of  the  iron  to  what  is  known  as  its  "  kindling 
point."  Now  quickly  introduce  the  hot  iron  into  a  jar  of 
oxygen.  It  will  burn  brilliantly,  throwing  off  bright,  glow- 
ing sparks,  and  the  iron  will  gradually  be  consumed  (Fig.  32). 
What  kind  of  substance  is  formed  when  the  iron  is  burned? 
Have  you  seen  this  substance  before  ? 

Oxygen  a  very  active  element.  These  experiments 
show  the  most  characteristic  property  of  oxygen.  It  is 
an  extremely  active  element,  and  the  experiments  you 
have  performed  should  suggest  to  your  mind  some 

1 A  watch  spring  which  has  been  heated  and  straightened  may  be 
used  in  this  experiment,  but  the  picture  cord  is  better. 


Oxygen  :   the  Active  Element  49 

interesting  queries.  If  the  atmosphere  were  composed 
entirely  of  oxygen,  would  not  the  stove  burn  as  well  as 
the  wood  in  it?  Why  does  not  this  happen  now  if  one 
fifth  of  the  air  is  pure  oxygen  ?  We  shall  find  an  answer 
to  the  last  question  when  we  study  the  nitrogen  of  the  air. 

Compounds  of  oxygen  called  oxids.  Oxygen  unites 
to  form  compounds  with  all  the  known  elements  except 
a  very  few.  These  compounds  are  called  oxids.  Thus, 
when  the  iron  burned  in  the  oxygen,  or  was  oxidized, 
iron  oxid  was  the  result,  a  compound  more  familiarly 
known  as  iron  rust.  The  metal  calcium  and  oxygen 
combine  to  form  calcium  oxid,  commonly  known  as 
lime ;  silicon  with  oxygen  forms  silicon  dioxid,  known  as 
silica,  or  sand,  and  so  on. 

The  meaning  of  "  id  "  in  chemistry.  Chemical  sub- 
stances that  have  names  ending  in  id  contain  elements 
that  are  mentioned  in  the  name  and  no  others.  Thus 
sodium  chlorid  (common  salt)  contains  only  sodium 
and  chlorin;  iron  sulfid,  only  iron  and  sulfur;  mag- 
nesium  oxid,  no  element  but  magnesium  and  oxygen. 

What  elements  do  the  following  compounds  contain: 
mercuric  oxid,  gold  chlorid,  hydrogen  sulfid,  potassium 
iodid,  iron  oxid,  carbon  dioxid,  sulfur  dioxid? 

Slow  oxidation.  Oxygen  oftentimes  unites  so  slowly 
and  gradually  with  other  elements  that  neither  light  nor 
intense  heat  is  produced.  These,  however,  are  none  the 
less  cases  of  oxidation,  or  combustion,  as  it  is  ordinarily 
called,  and  the  compounds  are  the  same  whether  the 
action  takes  place  slowly  or  rapidly.  A  house  pro- 
duces as  much  heat,  in  the  aggregate,  if  it  decays  by  slow 


Science  for  Beginners 


FIG.  33. 


A  retort  for  the  manufac- 
ture of  oxygen. 


oxidation  through  many 
years  as  it  does  if  it  is  con- 
sumed by  fire  in  an  hour  or 
two.  Cases  of  slow  oxida- 
tion are  all  about  us,  and  if 
you  are  wide  awake  you  will 
be  able  to  find  many  of 
them.  Explain  the  rusting 
knife  blade ;  the  ink  which 
is  first  pale  and  afterward 
bright  and  distinct ;  the 

wood  rotting  in  the  forest;  why  we  galvanize  our 
fences  and  roofs  and  paint  our  bridges  and  houses; 
and  why  we  constantly  fill  our  lungs  with  air. 

Oxidation  an  important  process.  How  do  we  obtain 
heat  to  warm  our  houses  and  power  to  run  our  machinery  ? 
Usually  by  oxidizing  wood  and  coal.  How  do  we  light 
our  houses  ?  By  oxidizing  gas  or  kerosene,  or  with  elec- 
tricity that  is  made  by  machinery  run  by  burning  wood  or 
coal.  What  happens  when  gasoline  explodes  in  the  engine 
of  an  automobile  ?  The  gasoline  suddenly  unites  with  the 
oxygen  of  the  air  which  has  been  drawn  into  the  cylinders. 
A  furnace  is  an  oxidizing  machine;  an  engine  is  an 
oxidizing  machine;  and  man  and  all  other  animals 
are  oxidizing  machines.  By  heat  secured  from  the  pro- 
cess of  oxidation  metals  are  melted ;  by  power  secured 
from  the  same  process  buildings  are  refrigerated  and 
water  is  frozen  to  ice.  Human  life  and  all  human 
activities  depend  upon  oxidation ;  without  oxygen  our 
lives  and  our  activities  would  cease. 


CHAPTER   SEVEN 

HYDROGEN  AND  ITS  COMPOUNDS 


FIG.  34.  Because  of  its  lightness, 
hydrogen  is  used  in  filling  airships 
and  balloons. 


HYDROGEN,  the  second  ele- 
ment that  we  shall  study,  is 
the  lightest  substance  known. 
It  is  about  14 J  times  as  light 
as  air,  11,160  times  as  light  as 
water,  and  151,700  times  as 
light  as  the  metal  mercury. 

It  enters  into  the  composition  of  all  plants  and  animals 
and  forms  part  of  wood,  coal,  and  petroleum,  but  the 
great  store  of  hydrogen  in  the  world  is  in  the  vast 
amounts  of  water  which  are  found  on  the  surface  of 
the  earth.  Hydrogen  occurs  in  a  free  state  in  the 
gases  from  some  volcanoes  and  natural-gas  wells,  and 
in  the  atmosphere  of  the  sun  and  of  some  fixed  stars. 
Because  of  its  lightness,  it  is  used  for  filling  airships  and 
balloons. 

Exercise  i.  Place  a  few  scraps  of  zinc  in  a  good-sized 
test  tube.  Fill  the  test  tube  half  full  of  water  and  pour  into 
it  a  few  drops  of  hydrochloric  or  sulfuric  acid.  A  gas  will 
be  seen  bubbling  up  through  the  liquid  and  escaping  into 
the  air.  This  gas  is  hydrogen. 

" 


Science  for  Beginners 


Bring  a  lighted  match  to  the 
mouth  of  the  tube  and  a  slight 
explosion  will  take  place.1 

Exercise  2.  Provide  the  tube 
with  a  tightly  fitting  cork  and 
a  delivery  tube.  After  all  the 
air  has  been  forced  out,  light 
the  gas.2  The  hydrogen  burns 
quietly  with  a  transparent  blue 
flame. 

Caution  I    Be  very  careful  not 

FIG.    35.      Hold   the    test    tube  ..  * 

away  from  the  body  and  with  its    to  nght  tne  gas  untl1  *"   the  air 

mouth  pointing  away  from  the   has  been  expelled  from  the  tube, 
e'  as  a  mixture  of  air  and  hydrogen 

forms  a  combination  that,  when  ignited, 
will  explode  with  very  great  violence. 

Exercise  3.  Hold  a  tumbler  or  re- 
ceiver that  is  both  dry  and  cold  over 
the  flame  of  burning  hydrogen  and 
notice  the  water  that  condenses  upon 
the  cool  surface.  What  is  uniting  with 

FIG.  36.  Be  careful  not  to  the  hydrogen  to  cause  it  to  burn  (Fig. 
37)?  What  evidence  does  this  afford 
as  to  the  composition  of  water? 


light  the  gas  until  all  the 
air  has  been  expelled  from 
the  tube  I 


1  In  this  and  other  experiments  the  test  tube  may  be  held  in  the  hand, 
provided  it  is  held  with  the  hand  extended  from  the  body  and  the  mouth 
of  the  test  tube  pointing  away  from  the  face  of  the  experimenter. 

2  To  determine  when  the  escaping  hydrogen  is  free  from  air,  fill  a 
small  test  tube  with  the  gas  as  directed  in  Exercise  4.    Then  close  the 
mouth  of  the  test  tube  with  the  thumb,  carry  it  a  short  distance  from 
the  generator,  and  holding  it  mouth  down  bring  a  lighted  match  or  taper 
to  the  mouth  of  the  tube.    If  only  a  slight  explosion  follows,  the  gas 
may  be  lighted. 


Hydrogen  and  Its  Compounds  53 


FIG.  37.    Condensing  water  that  is  formed  from  burning  hydrogen. 

Exercise  4.  Attach  a  piece  of  rubber  to  the  end  of  the 
delivery  tube  and  collect  the  gas  over  water  as  the  oxygen 
was  collected.  Fill  several  vessels  in  this  way. 

Exercise  5.  Carefully  and  slowly,  holding  it  with  its 
mouth  downward,  lift  a  tube  filled  with  the  gas.  (Why 
must  the  mouth  be  kept  down?)  Now  light  a  taper  and 
push  it  up  into  the  gas  (Fig.  39).  Two  things  will  happen : 
(i)  The  gas  will  be  ignited  at  the  mouth  of  the  tube  and 
will  burn  with  great  heat  but  with  an  almost  invisible  blue 
flame,  and  (2)  the  flame  of  the  taper  will  be  extinguished. 
If  the  taper  is  withdrawn,  it  will  be  relighted  at  the  mouth 
of  the  tube.  The  lighting  and  relighting  may  be  repeated 
several  times. 

This  experiment  has  shown  that  hydrogen  is  a  gas 
which  will  burn  but  will  not  support  combustion  in  other 
things. 

Exercise  6.  Fill  some  soap  bubbles  with  hydrogen  by  fit- 
ting a  clay  pipe  into  the  rubber  delivery  tube  from  which 


54 


Science  for  Beginners 


FIG.  38.     Collecting  hydrogen.  lerenCCS 

drogen  and  oxygen  are  the  following: 


hydrogen  is  being  pro- 
duced.1 After  a  bubble 
has  been  set  entirely  free 
from  the  generator,  bring 
a  lighted  taper  to  it. 
Explain  what  happens. 

Comparison  of  hydro- 
gen and  oxygen.  Some 
of  the  important  dif- 
ferences between  hy- 


HYDROGEN 

1.  It  is  lighter  than  air. 

2.  It  is  combustible. 

3.  It  will  not  support  com- 

bustion. 


OXYGEN 

1.  It  is  heavier  than  air. 

2.  It  is  not  combustible. 

3.  It  supports  combustion 

in  a  most  remarkable 
way. 


If,  now,  we  carry  the  comparison  further  and  contrast 
the  properties*  of  these  two  elements  with  the  properties 
of  the  water  which  is  formed  when  they  unite,  we  catch 
a  glimpse  of  a  very  important  and  far-reaching  chemical 
principle.  This  principle  will  be  discussed  in  the  next 
paragraph. 

Compounds  different  from  the  elements  that  compose 
them.  It  is  a  remarkable  fact  that  compounds  are  usu- 
ally utterly  unlike  the  elements  of  which  they  are  made. 
Thus,  the  properties  of  water  are  totally  different  from 
the  properties  of  the  oxygen  and  hydrogen  from  which 

1 A  little  glycerin  added  to  the  soapsuds  will  make  the  bubbles  tougher. 


Hydrogen  and  Its  Compounds 


55 


it  is  made;  yellow  sulfur  and  liquid 
mercury  form  a  red  powder  known  as 
vermilion ;  carbon,  a  solid,  combined 
with  nitrogen  and  hydrogen,  two  gases, 
forms  the  deadly  prussic  acid;  two 
solids,  black  carbon  and  yellow  sul- 
fur, when  chemically  united  form  a 
transparent  liquid  known  as  carbon 
disulfid;  the  poisonous  and  highly 
offensive  chlorin  gas,  which  has  been 
extensively  used  as  a  weapon  in  modern 
warfare,  combines  with  sodium,  a 
metal,  to  form  common  salt;  and  the  ,-, 

'  riG.    39.      Hydrogen 

limpid,  liquid  oil  of  turpentine  is  com-    bums  but  win  not 
posed  of  the  black  solid,  carbon,  and    support  combustion- 
the  gas,  hydrogen.     Some  of  the  compounds  mentioned 
may  be  found  in  the  chemical  laboratory,  and  the  last 
one  may  be  the  subject  of  an  interesting  experiment. 

A  study  of  turpentine.  With  very  simple  apparatus, 
oil  of  turpentine  can  be  broken  into  its  elements,  which 
are  very  different  from  itself.  This  is  done  in  Exercise 
7.  The  object  of  this  exercise  is  in  part  to  determine  the 
composition  of  turpentine,  but  more  especially  to  illus- 
trate the  fact  that  whenever  two  or  more  elements 
unite  by  chemical  action,  both  lose  the  properties  they 
originally  possessed  and  form  a  compound  having  en- 
tirely  different  properties. 

Exercise  7.  Obtain  a  small  quantity  of  .turpentine,  — 
five  cents'  worth,  —  such  as  is  used  in  mixing  paint.  Notice 
its  clearness,  transparency,  and  odor.  It  is  a  liquid,  easily 


Science  for  Beginners 


FIGS.  40  and  41. 

changing  to  a  gas  when  heated.  Fill  a  common  alcohol 
lamp  with  it.  A  small  bottle  with  a  cotton  wick  drawn 
through  the  cork  will  do. 

When  the  oil  has  filled  the  wick,  light  the  lamp  and  hold 
over  it  a  glass  tumbler.  The  glass  will  be  filled  with  a  great 
quantity  of  black  solid.  This  is  carbon,  which  must  have 
come  from  the  turpentine. 

Hydrogen  in  the  turpentine.  The  only  other  element 
contained  in  turpentine  is  hydrogen.  The  proof  of 
this  statement  would  not  be  within  the  reach  of  the 
beginner  in  chemistry,  and  he  will  have  to  take  the  word 
of  the  experienced  chemist.  Turpentine  is  a  compound 
of  carbon  and  hydrogen.  Its  composition  is  given  in 
the  formula  Ci0Hi6. 

Exercise  8.  Make  a  list  of  the  properties  of  carbon, 
hydrogen,  and  turpentine.  Do  the  carbon  and  hydrogen 
experience  a  total  loss  of  their  original  properties  when  they 
unite  chemically  to  form  turpentine? 


Hydrogen  and  Its  Compounds  57 

Three  classes  of  compounds.  Most  chemical  com- 
pounds can  be  classified  into  one  or  the  other  of  three 
groups.  These  groups  are  known  by  the  names  acids, 
bases,  and  salts.  As  acids  are  the  compounds  from 
which  hydrogen  must  be  obtained,  this  class  is  studied 
in  connection  with  that  element. 

Acids.  Acids  are  constantly  used  by  the  chemist, 
and  are  of  great  importance  in  many  industrial  pro- 
cesses. All  acids  contain  hydrogen,  which  is  set  free 
when  the  acid  comes  in  contact  with  a  metal.  Let  us 
now  investigate  this  very  important  class  of  substances. 

Exercise  9.  To  a  test  tube  half  full  of  water  add  not 
more  than  six  drops  of  hydrochloric  acid.  Mix  the  acid 
and  water  together  and  then  lift  out  a  small  drop  of  the  solu- 
tion with  a  glass  rod  and  touch  it  to  the  tongue.1  Could  you 
describe  the  taste  of  the  hydrochloric  acid?  Does  it  have  a 
sour  taste  ?  The  taste  is  due  to  the  hydrogen  which  is  set 
free  when  the  acid  is  dissolved  in  water. 

Exercise  10.  Put  a  little  piece  of  blue  litmus  paper  into 
the  mixture.  What  happens?  This  is  the  usual  test  for 
any  acid. 

Exercise  u.  Now  add  more  of  the  acid  to  the  water 
solution  and  into  this  drop  a  small  scrap  of  sheet  zinc  or 
magnesium.  Notice  the  bubbles  of  gas  which  rise  from  the 
surface  of  the  zinc  to  the  surface  of  the  water.  Bring  a 
lighted  match  to  the  mouth  of  the  test  tube.  A  slight 
explosion  takes  place.  The  chemist  recognizes  this  as  a 
sign  that  hydrogen  has  been  produced  (page  52). 

1  It  is  not  safe  to  taste  chemicals  in  the  laboratory  except  when 
advised  to  do  so  by  some  one  who  has  knowledge  of  the  chemical 
in  question. 


58  Science  for  Beginners 

The  chemist  reasons  that  since  zinc  is  an  element 
composed  of  that  metal  and  nothing  else,  the  hydrogen 
must  have  come  from  the  hydrochloric  acid.  His 
record  of  what  happened  in  the  above  experiment  is 
as  follows : 

Zn  +  2  HC1         ->  ZnCl2  +  H2 

zinc  +  hydrochloric  acid  produces  zinc-chlorid  +  hydrogen 

The  zinc  unites  with  the  chlorin  of  the  acid,  thus 
taking  the  place  of  the  hydrogen  and  setting  it  free. 

Exercise  12.  Repeat  the  last  three  exercises,  but  use 
sulfuric  acid  instead  of  hydrochloric  acid.  For  the  first 
two  exercises  use  not  more  than  three  drops  of  sulfuric  acid, 
and  for  the  last  exercise  nine  or  ten  drops.  Make  a  record 
of  these  tests  and  the  results. 

Exercise  13.  Repeat  the  three  tests,  but  use  strong  vine- 
gar, which  contains  a  well-known  acid  called  acetic  acid. 
Record  your  results. 

Properties  of  acids.  These  three  substances,  hydro- 
chloric acid,  sulfuric  acid,  and  vinegar,  are  repre- 
sentatives of  the  class  of  chemical  compounds  called 
acids,  of  which  there  is  a  very  large  number.  The 
properties  of  an  acid  are : 

1.  It  is  sour  to  the  taste. 

2.  It  turns  blue  litmus  paper  red. 

3.  It  contains  hydrogen,  which  can  be  set  free  by  the 
action  of  a  metal. 

In  the  majority  of  cases  the  litmus-paper  test  is  the 
only  one  that  need  be  made  in  order  to  detect  an  acid. 

Exercise  14.  Test  with  blue  litmus  paper  various  sub- 
stances to  be  found  about  the  laboratory  and  at  home,  such 


Hydrogen  and  Its  Compounds 


59 


as  lemon  juice,  sour  milk, 
saliva,  the  pulp  from  a 
gooseberry,  or  the  juice  of 
rhubarb. 

Exercise  15.  Dig  up 
some  soil  from  a  field  or 
garden  and  make  a  compact 
moist  ball  of  it.  Split  it 
open  and  place  a  piece  of 
blue  litmus  paper  in  it, 
leaving  the  paper  there  for 
a  few  minutes.  Many  crops 
do  not  grow  well  in  acid 
soil. 

The  up-to-date  farmer 

is    a     Scientist.      He    tests      FIG.  42.      The  up-to-date  farmer  tests 

his  soil,   and  if  he  finds  his  soil  with  litmus  paper. 

it  acid  he  "  sweetens  "  it  by  applying  finely  pulverized 
limestone,  marl,  or  air-slaked  lime.  In  later  chapters 
we  shall  have  occasion  to  refer  again  to  acids,  and  we 
shall  study  some  of  the  substances  that  have  the  power 
to  neutralize*  or  destroy  them. 

One  of  the  most  important  of  the  acids  is  hydrochloric 
acid,  a  compound  of  hydrogen  and  chlorin.  The  ele- 
ment chlorin  and  its  compounds  will  be  studied  in  a 
later  chapter. 


CHAPTER   EIGHT 

A  STUDY  OF  WATER 


FIG.  43.    Water  in  the  winter  time. 

WHAT  is  water?  This  question  may  seem  very  easy 
to  answer,  because  water  is  so  common  and  so  well 
known.  It  is  very  common,  but  is  it  well  known? 

Every  one  is  more  or  less  familiar  with  ice,  water, 
and  steam,  and  most  boys  and  girls  know  that  these 
are  thought  of,  not  as  three  different  things,  but  as 
three  different  forms  of  the  same  thing.  They  can 
readily  be  changed  from  one  of  the  forms  to  either  of 
the  other  two.  How? 

Exercise  i .  Write  a  description  of  water  as  it  is  found  out- 
of-doors  in  the  northern  part  of  the  United  States  during  the 
winter  time.  Read  up  on  the  subject  in  an  encyclopedia; 
at  least  consult  an  unabridged  dictionary. 

60 


A  Study  of  Water  61 

Exercise  2.  Write  a  second  description  of  water,  as  it 
appears  in  the  summer  time.  Consult  a  text  on  chemistry. 

Exercise  3.  Write  a  third  description  of  water,  as  it  is 
found  at  the  mouth  of  the  spout  of  a  teakettle  in  which  the 
water  is  boiling  vigorously.  Put  your  finger  cautiously 
into  what  appears  to  be  empty  space  at  the  mouth  of  the 
spout.  With  what  is  that  particular  space  filled?  Is  water 
vapor,  or  steam,  visible? 

After  escaping  steam  is  cooled  by  the  air,  it  condenses 
into  small  drops  which  make  a  cloud  or  fog  that  is  vis- 
ible. This  is  not  true  steam,  and  if  you  will  heat  it  by 
holding  a  flame  near  it,  the  droplets  of  water  will  again 
be  changed  into  invisible  vapor.  Real  steam  is  invisible. 


FIG.  44.     Real  steam  is  invisible. 

Occurrence  of  water.  We  may  find  water  in  some 
rather  unexpected  places.  Let  us  continue  to  study 
the  subject  and  ascertain  by  experience  some  facts 
concerning  the  occurrence  of  this  abundant  and  inter- 
esting substance. 


62  Science  for  Beginners 

Exercise  4.  Put  a  piece  of  raw  potato  in  a  test  tube  and 
heat  it  gently,  keeping  the  top  of  the  tube  cool.  What 
condenses*  along  the  sides  of  the  tube? 

Repeat  the  experiment  with  a  piece  of  ripe  apple.  Do  the 
same  with  a  piece  of  "  green  "  wood.  Now  try  a  bit  of  dry 
pine  shavings.  From  all  these  you  have  derived  water. 

Many  minerals,  rocks,  and  stones  contain  water,  as 
the  following  experiment  will  show: 

Exercise  5.  Obtain  samples  of  gypsum  (calcium  sulfate) 
and  blue  vitriol  (copper  sulfate),  and  gently  heat  each  of 
them  in  a  test  tube.  They  will  both  yield  water. 

The  bodies  of  all  animals  contain  a  large  amount  of 
water.  If  a  man  weighs  150  pounds,  at  least  90  pounds 
of  that  weight  is  water.  Lean  meat  contains  from  50 
to. 7 5  per  cent  of  water.  If  you  buy  4  pounds  of  meat, 
for  how  much  water  do  you  pay? 

Exercise  6.  Lean  steak  contains  on  an  average  8  per  cent 
bone,  and  65  per  cent  of  the  remainder  is  water ;  dried  beef 
contains  no  bone  and  is  about  45  per  cent  water.  Is  it 
cheaper  to  buy  steak  at  25  cents  a  pound  or  dried  beef  at 
40  cents  a  pound  ? 

The  facts  contained  in  the  following  table  will  give 
rise  to  other  interesting  questions : 

Bread  contains  about 35  per  cent  of  water 

Fresh  fish  (edible  portion)  contains  about     .  75-80  per  cent  of  water 

Flour  contains  about \2\  per  cent  of  water 

Apple  (edible  portion)  contains  about  ...  84  per  cent  of  water 

Turnip  (edible  portion)  contains  about     .     .  90  per  cent  of  water 

Watermelon  (edible  portion)  contains  about  92^  per  cent  of  water 

Cucumber  (edible  portion)  contains  about     .  95  per  cent  of  water 

A  jellyfish  contains  about 98.9  per  cent  of  water 


A  Study  of  Water  63 

The  water-holding  capacity  of  the  air.  Water  vapor 
is  a  part  of  the  atmosphere ;  some  of  it  is  always  present 
in  the  air.  The  amount  of  vapor  that  the  air  can  hold 
depends  on  the  temperature.  If  the  temperature  is 
high,  the  air  can  hold  as  much  as  4  ounces  of  water  in 
every  cubic  yard.  At  100  degrees  F.  it  holds  somewhat 
less  than  4  ounces;  at  80  degrees,  about  2  ounces; 
at  50  degrees,  a  little  over  three  quarters  of  an  ounce; 
and  at  the  freezing  point  of  water  (32  degrees)  it  holds 
slightly  more  than  one  third  ounce  per  cubic  yard. 

When  air  contains  as  much  water  vapor  as  it  can 
hold,  it  is  said  to  be  saturated.  Wha£  would  happen  if 
air  saturated  with  water  vapor  at-^QO  degrees  were 
suddenly  cooled  down  to  60  degree's?  What  happens 
every  time  the  air  becomes  saturated  and  the  tempera- 
ture falls? 

Exercise  6.  Compute  the  weight  of  water  contained  in  a 
room  that  is  21  by  36  feet  and  9  feet  high,  with  the  air  at  100 
degrees  F.  and  completely  saturated. 

Exercise  7.  What  does  your  geography  say  about  the 
proportion  of  land  and  water  on  the  surface  of  the  earth? 

Rain.  Large  bodies  of  water  like  the  Great  Lakes  and 
the  oceans  are  the  source  of  the  largest  part  of  the  water 
vapor  in  the  air.  As  the  vapor  rises  from  the  surface 
of  these  bodies  of  water,  it  is  carried  by  the  winds  out 
over  the  land.  It  is  next  condensed  into  clouds,  and 
under  certain  conditions  the  minute  droplets  of  water 
which  form  the  clouds  unite  into  larger  drops  and  fall 
as  rain.  What  becomes  of  clouds  when  they  disappear 
without  falling  as  rain?  About  eight  elevenths  of  the 


64  Science  for  Beginners 

water  that  falls  as  rain  flows  through  the  rivers  to  the 
sea. 

A  summer  shower.  Very  few  persons  stop  to  think 
of  the  great  amount  of  water  that  falls  in  an  ordinary 
shower.  A  very  light  shower  will  precipitate  perhaps 
one  one-hundredth  of  an  inch  of  water.  Not  very 
much,  you  say;  but  how  much  falls,  at  that  rate,  on 
the  surface  of  a  lot  50  by  100  feet?  Water  weighs 
62^  pounds  per  cubic  foot.  How  many  pounds  of  water 
will  the  very  light  shower  throw  down  upon  an  acre? 
How  much  upon  a  square  mile?  Heavy  rains  may 
give  a  depth  of  one  inch  per  hour  or  sometimes  more. 
What  will  be  the  total  weight  of  water  from  an  hour  of 
such  a  rain  upon  a  square  mile?  Upon  the  county 
or  city  in  which  you  live?  If  a  shower  precipitates 
one  fourth  of  an  inch,  how  much  would  the  water  upon 
a  square  mile  weigh? 

Rainfall.  It  is  very  interesting  to  know  the  depth  of 
the  annual  rainfall  for  the  locality  where  you  live  and 
to  know  the  time  of  the  year  when  most  of  the  rain 
falls,  as  upon  these  two  factors  depend  the  kind  and 
amount  of  the  crops  that  cafi  be  raised.  To  make  a 
rain  gauge  by  which  rainfall  can  be  measured,  place 
somewhere  out  in  the  open  a  rather  deep  vessel  with 
vertical  sides  (Fig.  122,  page  206).  The  most  accurate 
results  will  be  reached  if  the  vessel  is  buried  nearly  or 
quite  even  with  the  ground. 

Snow.  When  a  cloud  passes  into  air  that  is  below 
the  freezing  point  of  water,  the  droplets  of  water  are 
changed  to  small  ice  crystals.  These  little  crystals 


A  Study  of  Water 


FIG.  45.    Some  forms  of  snowflakes. 

unite  to  form  a  wonderful  variety  of  beautiful  six-sided 
stars  which  we  call  snowflakes.  Snowflakes  grow,  as 
they  fall,  by  condensing  additional  moisture  from  the 
air.  They  are  larger  in  mild  than  in  cold  weather. 
Over  1000  different  forms  of  snowflakes  have  been  ob- 
served. If  perfect  they  are  always  six-sided.  They 
form  best  in  still  air. 

Exercise  8.  Catch  snowflakes,  as  they  fall,  on  a  black 
cloth  or  paper  and  examine  their  forms.  Perhaps  you  can 
catch  the  snowflakes  on  your  coat  sleeve  on  the  way  to 
school.  A  magnifying  glass  will  be  helpful  in  determining 
the  forms  of  the  flakes. 

Sleet.  Snowflakes  lose  their  regular  form  when  they 
are  driven  about  by  a  wind,  and  if  this  occurs  when  the 
snow  is  just  on  the  point  of  melting  into  water,  sleet  is 
formed.  When  the  ground  is  colder  than  the  air,  the 
sleet  freezes  and  forms  a  coating  of  smooth  ice  upon  the 
ground  and  the  trees.  Although  this  condition  leads 
to  many  accidents,  it  furnishes  one  of  the  most  beautiful 
visions  of  the  winter  time  in  our  northern  states. 

A  snowfall.  The  amount  of  water  in  a  snowfall  is 
equal  to  about  one  tenth  of  its  depth.  Write  in  your 
notebook  all  the  good  results  you  can  think  of  that 


66  Science  for  Beginners 

follow  a  fall  of  snow  that  comes  and  remains  upon  the 
earth  for  weeks  or  months.  The  fall  of  snow  is  heaviest 
in  the  cool  temperate  regions.  Near  the  poles  there 
is  not  enough  moisture  in  the  air  for  heavy  snowfalls. 

The  sea.  What  per  cent  of  the  surface  of  the  earth 
is  covered  by  water?  Name  the  oceans  in  the  order  of 
their  size,  beginning  with  the  smallest. 

What  is  the  greatest  width  of  the  Pacific  Ocean  in 
miles?  How  far  is  it  from  San  Francisco  to  Honolulu? 
From  New  York  to  Liverpool?  From  New  York  to 
Buenos  Aires?  What  have  you  learned  concerning 
the  depth  of  the  water  of  the  oceans?  Is  the  land 
under  the  sea  diversified  into  mountains,  valleys,  and 
plains  ?  How  do  the  depths  of  the  sea  compare  with  the 
heights  of  the  land  areas  ? 

Water  a  powerful  solvent.  Water  is  everywhere 
acting  to  dissolve  the  various  materials  with  which  it 
comes  in  contact.  Scarcely  anything  escapes  its  sol- 
vent* power.  The  water  which  falls  from  the  clouds  in 
rain  or  snow  is  quite  free  from  foreign  substances ;  but 
after  falling  on  the  earth  and  soaking  into  the  ground, 
it  becomes  filled  with  many  substances  that  have  been 
dissolved  in  it. 

Exercise  9.  Put  a  lump  of  sugar  in  water.  The  liquid 
will  enter  into  the  sugar  until  it  has  passed  into  every  por- 
tion of  it.  If  there  is  enough  water  present,  the  sugar  will 
entirely  disappear  in  the  water,  forming  a  solution  of  sugar 
in  water.  If  any  portion  of  the  solution  is  tested  by  the 
sense  of  taste,  it  will  be  found  to  be  sweet,  thus  showing  how 
complete  the  solution  is. 


A  Study  of  Water  67 

Exercise  10.  Place  some  clean,  clear  water  from  a  well 
or  spring  in  an  evaporating  dish  and  boil  it  until  the  water  is 
gone.  Usually  a  whitish  residue*  will  remain.  This  is  the 
mineral  matter  that  was  in  the  water.  Is  the  inside  of  the 
teakettle  that  is  used  in  your  kitchen  coated  with  mineral 
matter  ? 

Because  of  its  solvent  power  water  often  hollows  out 
great  caves  in  the  earth,  and  all  our  rains  carry  large 
amounts  of  minerals  to  the  sea.  What  becomes  of  these 
minerals  when  the  water  is  evaporated  from  the  ocean? 
Where  did  the  salt  in  the  ocean  come  from?  - 

The  solvent  power  of  water  increased  by  heat  and 
carbon  dioxid.  The  solvent  power  of  water  is  greatly 
increased  by  increasing  the  temperature,  and  for  this 
reason  water  that  finds  its  way  deep  down  into  the  earth, 
where  the  temperature  is  high,  will  dissolve  much  more 
of  the  solid  minerals  and  rocks  than  it  could  dissolve  at 
the  surface  of  the  earth.  Again,  when  water  has  fallen 
upon  the  earth  and  passed  through  the  soil  it  becomes 
charged  with  certain  gases,  especially  carbon  dioxid, 
by  means  of  which  it  will  then  dissolve  solid  limestone 
(page  148). 

Sometimes  water  that  has  gone  to  great  depths  in 
the  earth  may  come  to  the  surface  again  with  more 
mineral  matter  than  it  can  hold  in  solution,  so  that, 
when  it  cools  and  the  carbon  dioxid  in  it  escapes,  the 
mineral  matter  is  deposited.  If  this  water  comes  into 
a  cave  or  cavern,  the  water  drips  from  the  roof  and 
is  evaporated,  leaving  the  limestone  in  the  form  of 
stalactites*  or  stalagmites*.  If  the  water  issues  as  a 


68 


Science  for  Beginners 


FIG.  46.    Mineral  matter  deposited  by  the  waters  of  a  hot  spring  in  Yellow- 
stone National  Park. 

hot  spring,  very  beautiful  mineral  deposits  may  be  built 
about  the  mouth  of  the  spring. 

Organic  matter  in  water.  Water  from  a  swamp  or 
stagnant  pool  is  usually  brown  or  black  in  color.  This 
color  is  due  to  the  presence  of  organic  or  vegetable 
matter. 

Exercise  n.  Evaporate  to  dryness  a  vessel  of  water  from 
a  swamp  or  stagnant  pool.  Note  the  dark-colored  organic 
matter  which  remains.  Heat  the  residue  very  hot,  and  the 
organic  matter  will  all  be  burned  out.  The  gray  or  white 
ash  which  remains  is  mineral  matter. 

Disease  germs  in  water.  The  disease  germs  that 
attack  us  are  little  plants  and  animals, — plants  and 
animals  so  small  that  they  can  be  seen  only  through  a 
powerful  microscope.  Their  home  is  in  the  human  body, 
where  they  live  surrounded  by  the  fluids  of  the  body. 
They  are  adapted  to  a  liquid  habitat*,  and  drying  is 
fatal  to  them.  When  they  reach  the  outside  world, 


A  Study  of  Water  69 

therefore,  they  quickly  die  in  such  places  as  the  dust  of 
streets.  If  germs  get  into  water,  however,  many  of 
them  live  for  a  number  of  days.  This  makes  water 
particularly  dangerous  as  a  carrier  of  germs,  and  care 
must  be  taken  to  exclude  germs  from  drinking  water. 
Like  other  plants  and  animals,  disease  germs  are  killed 
by  heat,  and  if  water  is  heated  for  a  few  minutes  to 
150  degrees,  any  germs  of  human  disease  that  are  in  it 
will  die.  Bringing  water  to  the  boiling  point  will  make 
it  safe  for  drinking  purposes. 

Exercise  12.  Boil  a  flask  of  water  for  half  an  hour.  Allow 
it  to  cool  and  then  drink  some  of  it.  Note  the  "  flat "  taste. 
Heat  another  flask  of  water,  but  remove  it  from  the  fire 
as  soon  as  bubbles  of  steam  begin  to  appear  in  it.  Cool  it 
and  note  the  taste.  The  flat  taste  in  boiled  water  is  due  to 
the  air  having  been  driven  out.  If  water  is  brought  just  to 
the  boiling  point,  its  drinking  qualities  will  not  be  impaired 
and  yet  the  germs  in  it  will  be  killed. 

Where  does  a  fish  get  the  oxygen  that  it  must 
have,  in  order  to  sustain  its  life?  Why  does  the  por- 
poise* or  the  whale  come  to  the  top  of  the  water  to 
breathe? 

A  study  of  the  chemical  composition  of  water.  There 
is  a  very  instructive  experiment  which  will  interest  you, 
though  you  may  not  possess  the  apparatus  for  making 
it  yourself  (Fig.  47).  It  will  answer  an  important  ques- 
tion which  the  chemist  is  always  asking,  not  only  about 
water,  but  about  every  substance  in  which  he  becomes 
interested.  This  question  is:  Of  what  is  it  composed? 
The  ancients  called  water  an  element  because  they 


Science  for  Beginners 


—  -*•—•-  1 1       _r  --  -  ._  jn: .      ._L.__  f ""    ---'    --•-  — •-- 

FIG.  47.    The  liquid  water  is  broken  up  into  two  gases, 
hydrogen  and  oxygen. 

knew  no  method  by  which  it  could  be  resolved  into 
anything  more  simple  than  itself. 

Breaking  water  into  two  gases.  Figure  47  shows  an 
apparatus  for  decomposing  water.  It  consists  of  a  bat- 
tery of  electric  cells,  the  wires  of  which  end  in  plati- 
num strips,  called  electrodes.  These  electrodes  are  in 
the  open  ends  of  test  tubes  which  have  previously  been 
filled  with  water  to  which  a  small  amount  of  sulfuric 
acid  has  been  added.  The  water  between  the  test  tubes 
forms  part  of  the  circuit  of  the  battery,  and  when  the 
current  begins  to  flow,  the  electricity  passes  from  one 
electrode  to  the  other  through  the  water.  When  this 
happens,  the  molecules  of  water  are  broken  up  and 
bubbles  of  gas  are  seen  rising  in  the  test  tubes.  It  will 


A  Study  of  Water  71 

be  noticed  that  the  gas  collects  in  one  of  the  tubes  about 
twice  as  fast  as  in  the  other. 

The  gases  formed  from  water.  The  question  of  the 
chemist  is  not  yet  answered,  and  it  will  not  be  until  he 
finds  out  the  character  and  names  of  the  two  gases. 

If  the  tests  described  on  page  52  are  repeated  with  the 
gas  which  collects  in  the  greatest  quantities,  it  will  be 
found  that  this  gas  is  hydrogen.  The  experiment  has 
taught  us,  therefore,  that  water  is  in  part  composed  of 
hydrogen.  We  have  also  observed  that  of  the  entire 
amount  of  gas  obtained  from  the  water,  two  thirds  of  it, 
measured  by  volume,  is  hydrogen. 

Read  the  experiments  described  on  page  46  and  make 
the  same  test  on  the  gas  in  the  second  tube.  It  will 
be  found  that  this  gas  is  oxygen.  Water  is  in  part 
composed  of  oxygen. 

In  Exercise  3  on  page  52,  hydrogen  and  the  oxygen  of 
the  air  were  made  to  unite,  and  the  product  of  their 
combination  was  water.  Putting  that  fact  with  what 
we  have  just  learned,  we  conclude  that  water  is  a  com- 
pound  formed  by  the  chemical  union  of  the  two  gases, 
hydrogen  and  oxygen.  Each  molecule  of  water  con- 
tains two  atoms  of  hydrogen  and  one  atom  of  oxygen. 
The  chemical  formula  is  H2O. 

Can  you  explain  why  the  study  of  water  properly 
follows  the  study  of  oxygen  and  hydrogen? 


CHAPTER  NINE 

A  PINCH  OF  SALT 


FIG.  48.  Manufacturing  salt  in  Syracuse,  New  York.  The  brine  is  pumped 
from  deep  welk  and  evaporated  by  the  heat  of  the  sun.  The  covers  shown 
along  the  sides  are  turned  down  over  the  tables  at  night  and  during  rains. 

THERE  is  no  substance  in  common  life  which  is  of 
greater  importance,  or  which  will  better  repay  careful 
study,  than  common  salt.  We  know  its  value  in  our 
daily  food;  without  it  the  food  would  be  insipid*  and 
tasteless.  Animals  not  only  do  not  thrive  but  cannot 
even  live  when  deprived  of  salt  for  any  length  of  time. 
Its  qualities  of  preservation  are  well  known  to  us,  as 
they  were  to  the  ancients,  who  used  it  in  sacrifices.  An- 
cient philosophers  and  poets  have  spoken  or  sung  its 
praises,  and  to  the  present  day  the  Arabs  and  Russians 
use  it  as  the  emblem  of  hospitality.  Among  some  tribes 
of  barbarous  men,  who  are  otherwise  very  treacherous, 

72 


A  Pinch  of  Salt 


73 


the  traveler  is  safe  if  he  has  once  partaken  of  their  salt. 
We  shall  also  see  that  common  salt  is  the  starting  point 
and  the  basis  of  many  important  commercial  industries. 
Occurrence.  Salt  is  one  of  the  most  widely  distrib- 
uted substances  in  all  the  world.  It  is  found  in  the 
soil,  in  many  rocks,  in  brooks  and  rivers,  and  in  large 
amounts  in  the  sea.  It  is  found  in  inland  lakes,  like 
Great  Salt  Lake,  that  have  no  outlet;  the  waters  es- 
cape by  evaporation,  leaving  the  salt  behind.  The 
common  salt  of  commerce  is  obtained,  in  the  United 
States,  from  deposits  in  New  York,  Kansas,  Utah,  Michi- 
gan, Louisiana,  and  numerous  other  districts.  In  many 
places  the  salt  is  dissolved  in  water,  forming  brines* 
which  are  evaporated  to  obtain  the  solid  salt.  When  the 
brine  is  allowed  to  evaporate  slowly  by  the  help  of  the 
sun's  heat,  it  forms  large  crystals  which  are  sold  in  the 


FIG.  49.    Mining  rock  salt. 


74  Science  for  Beginners 

_ 

market  as  "  solar*  salt."  Crystals  of  greater  purity 
can  be  obtained  by  using  artificial  heat  and  constantly 
stirring  the  solution.  To  purify  our  coarse  salt  for  table 
use,  the  bitter  ingredient  of  magnesium  chlorid  must 
be  removed. 

Exercise  i.  Procure  samples  of  refined  table  salt  and 
also  of  the  common  cheap  salt  that  is  sold  by  the  barrel. 
It  may  also  be  possible  to  procure  a  small  piece  of  rock  salt. 
Ascertain  the  current  market  prices  for  each  of  these  grades, 
as  that  will  be  one  way  of  judging  of  their  relative  purity. 

Exercise  2.  Test  the  three  varieties  of  salt  as  to  taste. 
Do  you  notice  a  difference?  Which  contains  the  most  pro- 
nounced bitter  taste  ? 

Can  you  describe  a  taste?  Suppose  that  some  one 
did  not  possess  the  sense  of  taste;  could  you  describe 
the  taste  of  salt  to  him  so  that  he  would  understand  it? 
Taste  can  be  learned  only  by  experience. 

Exercise  3.  Examine  a  small  portion  of  the  table  salt. 
Is  it  solid,  liquid,  or  gaseous?  What  is  its  color?  Is  it 
malleable  or  brittle? 

Exercise  4.  Test  the  solubility*  of  common  salt  by  plac- 
ing it  in  water  and  noting  how  readily  it  dissolves.  Already, 
in  Exercise  2,  you  have  made  one  experiment  bearing  on  this 
point.  What  must  always  happen  to  any  substance  before 
it  will  have  a  taste?  Why  is  it  that  a  clean  stone,  placed 
on  the  tongue,  gives  no  taste?  Add  more  salt  to  the  water. 
Is  it  readily  or  not  readily  soluble  in  water  ?  Some  substances 
are  insoluble  in  water. 

This  question  as  to  the  solubility  of  substances, 
whether  they  are  soluble  or  insoluble,  is  one  of  the  most 
important  ones  with  which  the  chemist  has  to  deal.  If 


A  Pinch  of  Salt 


75 


he  knows  the  solubility  of  the  different  substances  he 
is  handling,  he  is  often  able  to  foretell  what  the  chem- 
ical action  will  be. 

Exercise  5.  Spread  some  table  salt  on  a  black  paper  and 
examine  the  particles  with  a  magnifying  glass.  Are  they 
regular  in  shape  ? 

Exercise  6.  Place  a  small  amount  of  a  salt  solution  in  an 
evaporating  dish  and  evaporate  the  water.  If  more  con- 
venient, the  solution  may 
be  placed  in  a  plate  or 
saucer  and  the  water 
evaporated  by  setting  the 
vessel  in  the  sun  or  near 
a  stove.  When  the  water 
is  nearly  all  gone,  examine 
and  describe  the  crystals* 

Of  Salt.  Well-formed  Salt 
Crystals  are  usually  per- 
feet  Cubes*  (Fig  S2) 

The   physical   proper- 

ties-  of  salt.     Now  put 


FIG.  50.  By  filtration  the  chemist  sepa- 
rates  insoluble  solids  from  liquids.  He  also 
separates  in  this  way  soluble  and  insoluble 
solids.  The  illustration  shows  how  a  filter 
paper  is  folded  and  placed  in  the  funnel. 


into  a  single  sentence 
the  facts  you  have  learned  concerning  salt.  You  have 
made  a  list  of  the  physical  properties  of  this  substance  ; 
you  can  define  salt  from  the  standpoint  of  physics. 
What  is  salt  ?  Your  answer  may  be  that  salt  is  a  white, 
crystalline*  solid,  very  brittle,  not  malleable,  soluble  in 
water,  and  with  a  peculiar  taste. 

A  chemical  study  of  salt.  When  a  chemist  is  working 
with  a  substance,  he  is  almost  entirely  concerned  with 
asking  and  answering  two  questions.  The  first  question 


76  Science  for  Beginners 

is :  Of  what  is  it  made  ?  The  second  question  is :  How 
will  the  substance  behave,  or,  what  will  be  formed  from 
it,  when  it  is  brought  into  contact  with  other  substances  ? 
After  the  chemist  has  answered  these  questions,  the 
practical  man  of  affairs  —  the  manufacturer,  the  physi- 
cian, the  farmer,  and  others  —  will  ask  what  the  sub- 
stance is  good  for.  It  will  thus  be  seen  that  the  chemist 
prepares  the  way  for  nearly  all  the  activities  of  agri- 
cultural, industrial,  and  commercial  life.  Let  us  now 
extend  our  investigation  of  salt  by  studying  it  according 
to  the  methods  of  chemistry. 

Exercise  7.  Place  a  small  amount  of  salt  in  a  test  tube 
and  add  a  few  drops  of  sulfuric  acid.  Is  there  evidence  of  a 
chemical  change?  Smell  the  gas  which  comes  from  the 
mixture,  but  do  not  inhale  too  much  of  it.  Notice  the  sharp, 
penetrating  character  of  the  gas;  it  is  as  if  the  point  of  a 
needle  had  been  thrust  into  the  nose.  Blow  the  moisture 
of  your  breath  across  the  mouth  of  the  test  tube  and  notice 
the  white  cloud  which  is  produced.  Hold  a  moist  piece  of 
blue  litmus  paper  in  the  gas. 

You  now  have  several  facts  to  add  to  your  definition 
of  common  salt.  You  can  say  that  common  salt  is  a 
white,  crystalline  solid ;  is  soluble  in  water ;  has  a  peculiar 
taste ;  is  not  malleable,  but  brittle ;  and  also  that  when 
treated  with  sulfuric  acid  it  yields  a  sharp,  penetrating 
acid  gas  which  is  somewhat  soluble  in  the  moisture 
of  the  breath  and  is  made  visible  by  this  moisture. 

Hydrochloric  acid.  The  gas  produced  in  the  above 
experiment  is  hydrochloric  acid.  It  may  be  recognized 
by  its  peculiar  odor  and  the  change  produced  by  the 


A  Pinch  of  Salt 


77 


breath.  This  acid  is  a  gas  and  when  dry  possesses  no 
acid  properties.  It  is  collected  and  kept  for  use  by 
passing  it  into  pure  water.  What  we  buy  at  the  drug 
store,  therefore,  is  a  solution  of  hydrochloric  acid  in 
water.  It  is  a  most  important  chemical  product  that 
has  extensive  applica- 
tions in  chemical  and 
other  industries. 

The  flame  test.  The 
flame  test  is  much  used 
by  chemists  to  determine 
the  elements  that  are 
present  in  a  substance. 
Make  the  flame  test  on 
salt  in  the  following 
manner : 

Exercise  8.  Dip  a  plati- 
num or  iron  wire  with  a 
small  loop  in  the  end  into  a  solution  of  salt  and  then  bring  it 
into  the  edge  of  the  colorless  part  of  a  gas  or  lamp  flame.  An 
instantaneous*  flash  of  a  brilliant  yellow  color  is  seen. 
Repeat  this  test  until  you  have  become  thoroughly  ac- 
quainted with  the  peculiar  yellow  color. 

Whenever  the  chemist  sees  this  yellow  color  in  the 
flame,  he  knows  that  he  is  dealing  with  a  substance  that 
contains  sodium.  The  ending  "  ium  "  indicates  that 
the  substance  which  bears  such  a  name  is  a  metal. 
Potassium,  magnesium,  calcium,  and  barium  are  metals, 
and  from  the  ending  of  its  name  we  may  know  that 
sodium  also  is  a  metal. 


FIG.  51.    The  flame  test. 


78  Science  for  Beginners 

Our  definition  of  salt  may  now  be  enlarged  to  include 
the  fact  that  it  is  in  part  composed  of  sodium.  We  may 
state  that  it  is  a  white,  crystalline,  brittle  solid,  soluble 
in  water,  has  a  peculiar  taste,  is  acted  upon  by  sulfuric 
acid,  giving  rise  to  a  strong,  penetrating,  odorous  gas, 
and  also  gives  the  flame  test  for  the  metal,  sodium. 

Composition  of  salt.  We  have  now  found  that  salt 
is  a  compound  of  sodium.  The  question  which  remains 
to  be  settled  is,  what  substance  is  combined  with  the 
sodium  to  produce  salt.  The  method  of  determining  this 
is  somewhat  complicated,  but  any  clear-headed  person 
can  make  some  experiments,  do  a  little  thinking  for  him- 
self, and  draw  conclusions  that  will  be  quite  satisfactory. 

Exercise  9.  Take  a  small  pinch  of  salt  and  mix  with  it 
a  like  amount  of  black  oxid  of  manganese  (MnO2).  Place 
in  a  test  tube  the  mixture  you  have  prepared.  Notice  that, 
as  far  as  you  can  see,  there  is  no  action  of  any  kind  between 
the  parts  of  the  mixture.  Now  pour  a  few  drops  of  sulfuric 
acid  on  the  mixture  and  warm  it  a  little  by  holding  the  tube 
near  the  flame  of  a  lamp  but  not  in  the  flame.  A  greenish 
yellow  gas  with  a  strong  and  disagreeable  odor  is  given  off. 
Do  not  inhale*  any  of  the  gas. 

Is  the  gas  that  is  given  off  hydrochloric  acid  ?  If  you 
cannot  readily  decide,  take  some  salt  in  another  test 
tube,  put  the  sulfuric  acid  on  it,  and  compare  the  two 
gases.  You  will  conclude  that  the  gas  given  off  when  the 
manganese  oxid  is  present  is  not  the  same  as  the  hydro- 
chloric acid  produced  when  it  is  not  present.  The  first 
gas  is  chlorin.  Its  symbol  is  Cl. 

Where  did  the  chlorin  come  from?     Could  it  have 


A  Pinch  of  Salt  79 

come  from  the  manganese  oxid?  This  substance  con- 
tains the  metal  manganese  and  only  one  other  element. 
What  is  that  element?  What  does  the  ending  "  id  " 
signify  to  the  chemist?  The  chlorin  could  not  have 
come  from  the  manganese  oxid.  It  could  not  have 
come  from  the  sulfuric  acid  (H2SO4)  because  that  is 
composed  only  of  hydrogen,  sulfur,  and  oxygen.  You 
conclude  that  the  chlorin  must  have  come  from  the  salt, 
and  your  conclusion  is  correct. 

Now,  from  our  entire  study  of  common  salt  we  may 
conclude  that  it  is  a  compound  produced  by  the  com- 
bination of  the  metal  sodium  with  chlorin.  In  other 
words,  the  white  solid  which  we  call  salt  is  formed  from 
a  shining,  soft  metal  that  burns  on  water  (page  86),  and 
a  greenish  yellow  gas.  This  fact  is  expressed  by  the 
chemical  formula,  NaCl.  The  chemical  name  of  salt  is 
sodium  chlorid.  It  is  very  fortunate  for  us  who  use 
the  salt  that,  in  combining,  both  sodium  and  chlorin 
lose  their  peculiar  properties. 

You  may  again  enlarge  your  definition  of  common 
salt  so  as  to  include  all  the  physical  and  chemical  prop- 
erties you  have  learned.  Do  this  and  enter  the  definition 
in  your  notebook.  No  other  substance  with  which  we 
are  acquainted  possesses  just  these  properties ;  and 
whenever  you  find  a  substance  having  these  exact  prop- 
erties, that  substance  is  common  salt. 

Exercise  10.  Repeat  Exercise  7,  using  about  a  level  tea- 
spoonful  of  salt  and  an  equal  amount  of  sulfuric  acid.  After 
the  hydrochloric  acid  has  all  been  given  off,  pour  the  con- 
tents of  the  test  tube  into  an  evaporating  dish  and  evaporate 


8o  Science  for  Beginners 


ROCK  SALT  FELDSPAR        QUART2         ICELAND  SPAR 

FIG.  52.    A  group  of  crystals. 

to  dryness.    The  white  substance  remaining  in  the  dish  is 
sodium  sulfate,  or  "  salt  cake." 

The  chemical  action  in  this  case  is  as  follows : 
2  NaCl  +  H2SO4  ->    2  HC1     +         Na*SO4 

salt          +  sulfuric  acid  — >•  hydrochloric  acid  +  sodium  sulfate,  or  "  salt  cake  " 

By  carefully  considering  this  case  of  chemical  action 
we  shall  see  that  the  sodium  and  the  hydrogen  have  ex- 
changed places,  and  that  by  this  action  hydrochloric 
acid  and  salt  cake  are  produced.  This  is  a  good  illus- 
tration of  what  occurs  in  thousands  of  other  cases 
when  one  chemical  acts  upon  another. 

Chemistry  closely  related  to  industrial  life.  It  is  a 
most  interesting  fact  that  the  chemist  in  his  laboratory 
is  all  the  time  teaching  processes  which  are  used  in  great 
industrial  plants  where  millions  of  dollars  are  expended 
and  thousands  of  men  are  employed.  For  example, 
salt  cake  and  hydrochloric  acid  are  produced  in  great 
manufacturing  plants  by  adding  sulfuric  acid  to  com- 
mon salt,  the  exact  method  we  were  using  in  the  above 
experiment.  The  hydrochloric  acid  is  employed  in 
many  chemical  and  industrial  processes,  and  great 
quantities  of  the  salt  cake  are  used  in  making  glass  and 
soda.  Salt  is  also  used  in  the  manufacture  of  many 


A  Pinch  of  Salt 


81 


other  valuable  products :  chlorates  for  explosives ; 
chlorin  for  bleaching  powder;  caustic  soda,  valuable 
for  many  purposes ;  soap ;  pottery ;  and  a  hundred 
other  products,  all  of  which  minister  to  our  comfort 
and  our  needs.  Perhaps  some  day  you  will  be  head 
chemist  in  a  great  manufacturing  establishment  where 
some  of  these  products  are  made. 

A  study  of  crystals.  In  Exercise  6  we  discovered 
one  of  Mother  Nature's  most  interesting  secrets.  When 
the  salt  was  allowed  to  solidify,  crystals  were  formed 
which  were  very  uniform  as  to  shape.  Of  what  shape 
were  they? 

Crystals  of  other  mineral  substances  also  are  very 
abundant ;  for  it  is  the  almost  invariable  rule  that  when 
any  substance  in  the  liquid  form  is  changed  to  a  solid, 
it  takes  a  crystalline  form.  If  the  conditions  are  favor- 
able, all  the  crystals  formed  from  a  given  substance  are  of 
exactly  the  same  shape  and 
all  have  the  same  number 
of  faces  of  the  same  form. 

Exercise  u.  Dissolve  as 
much  common  alum  in  hot 
water  as  the  water  will  hold. 
Suspend  a  string  in  this 
saturated  solution  and  set  it 
where  it  will  be  as  quiet  as 
possible.  It  is  best  to  hang 
a  small  weight  at  the  end  of 
the  string  to  help  hold  it  still.  After  the  solution  has  stood 
for  several  hours,  there  will  be  crystals  of  alum  upon  the  string. 


FIG.  53.    A  crystal  of  alum. 


82 


Science  for  Beginners 


Study  the  form  of  the  crystals.  How  many  and  what  shaped 
faces  has  each  ?  how  many  edges  ? 

When  the  crystals  cease  growing,  suspend  them  in  a  fresh 
solution.  In  this  way  larger  crystals  may  be  obtained. 

Exercise  12.  Repeat  the  above  experiments,  using  sugar. 
Crystals  of  "  rock  candy  "  will  be  formed.  Copper  sulfate 
may  be  used,  but  the  plan  of  the  crystal  is  not  readily  seen. 

The  different  crystals  of  the  same  substance  will 
not  be  of  the  same  size,  but  they  will  all  be  of  the  same 
shape.  If  there  is  too  much  material 
confined  in  a  given  space,  so  that  there 
is  not  room  enough  for  the  formation 
of  perfect  crystals,  there  will  still  be 
an  attempt  to  form  crystals ;  but  in 
this  case  there  will  be  a  great  number 
of  imperfect  crystals  joined  together 
in  one  mass.  Such  a  solid  is  said  to 
be  crystalline.  Many  of  our  rocks 
are  solids  of  this  kind. 
It  is  not  an  easy  thing  to  find  perfect  crystals,  al- 
though almost  every  locality  will  afford  specimens  of 
some  kinds  of  crystals,  and  the  sharp  eyes  of  an  in- 
terested observer  will  find  them.  Some  of  the  most 
beautiful  crystals  are  the  precious  gems.  Such  are  the 
diamond,  the  ruby,  the  emerald,  and  the  sapphire. 
These  and  others  are  very  beautiful ;  and  because  they 
are  hard  to  find,  they  command  a  great  price.  All  impor- 
tant museums  have  collections  of  wonderful  crystals  of 
hundreds  of  different  kinds.  If  possible,  visit  such  a 
museum  sometime  and  see  these  beautiful  objects. 


FIG.  54.  A  crystal  of 
copper  sulfate.  Per- 
fect crystals  of  this 
substance  are  rarely 
formed. 


CHAPTER  TEN 


CHLORIN  AND  SODIUM 


THE  study  of  salt  as 
a  compound  of  sodium 
and  chlorin  suggests 
that  it  would  be  of 
interest  to  make  a  fur- 
ther study  of  the 
elements,  chlorin  and 
sodium,  of  which  the 
salt  is  composed.  One 
purpose  in  making  the 
study  is  to  learn  some- 
thing more  of  two  very 
common  elements. 
Another  purpose  is  to 
gain  additional  knowl- 
edge of  some  chemical 
processes  that  are  of 


FIG.  55.    Preparing  and  collecting  chlorin. 


great  importance  in  our  daily  life. 

Preparation  of  chlorin.  One  method  of  producing 
chlorin  was  given  on  page  78.  Chlorin  may  be  obtained 
from  hydrochloric  acid  also  by  combining  that  acid  with 
potassium  chlorate. 

Exercise  i.  Put  a  small  piece  (of  the  size  of  a  kernel 
of  wheat)  of  potassium  chlorate  in  a  glass  flask  or  test  tube. 
Cover  it  with  a  few  drops  of  hydrochloric  acid  and  warm 
gently.  The  gas,  chlorin,  will  be  given  off.  It  may  be 
dissolved  by  pouring  water  upon  it,  or  it  may  be  collected 
in  a  jar  by  downward  displacement  of  air,  as  shown  in 
Figure  55. 

83 


Science  for  Beginners 


FIG.  56.  When  powdered  iron  is 
thrown  into  a  jar  of  chlorin,  a 
shower  of  sparks  is  produced. 


Properties   of   chlorin.     At 

ordinary  temperatures  chlorin 
is  a  greenish  yellow  gas  and 
has  a  peculiarly  disagreeable 
odor.  At  low  temperatures 
and  under  pressure  it  becomes 
a  liquid,  and  tanks  of  liquid 
chlorin  are  bought  and  sold. 
It  is  an  active  element,  com- 
bining with  many  substances, 
as  you  can  prove  by  experi- 
ment. Do  not  inhale  it,  as  it 
produces  a  feeling  of  suffoca- 
tion and  causes  coughing  and 
intense  irritation  of  the  eyes, 
nose,  and  throat.1 

Exercise  2 .  Throw  a  small  quantity  of  powdered  antimony, 
or  iron  powder,  into  a  jar  of  chlorin.  A  shower  of  brilliant 
sparks  is  produced  as  the  two  elements  combine  (Fig.  56). 

Exercise  3.  Moisten  a  piece  of  paper  with  oil  of  turpentine 
which  has  been  slightly  warmed  and  drop  the  paper  into  a 
jar  or  flask  containing  chlorin.  Observe  what  happens 
(Fig.  57)- 

You  have  already  learned  that  turpentine  is  a  com- 
pound of  carbon  and  hydrogen.  The  chlorin  has  a 
strong  affinity*  for  hydrogen  and  unites  with  the  hydro- 
gen of  the  turpentine,  setting  the  carbon  free.  What  sub- 
stance is  formed  when  chlorin  and  hydrogen  combine? 

1  Make  it  a  practice,  when  you  leave  the  chemical  laboratory,  to  go 
out  into  the  open  air  and  "wash  out"  your  throat  and  lungs  with  deep 
inhalations  of  pure  air. 


Chlorin  and  Sodium  85 

An  experiment  in  bleaching  cloth  will  also  show 
the  strong  tendency  of  chlorin  to  unite  with  hydro- 
gen. 

Experiment  4.  Moisten  a  piece  of  colored  cloth  and  place 
it  in  a  jar  of  chlorin.  The  color  will  slowly  be  removed  from 
the  cloth. 

Repeat  the  experiment  with  a  colored  flower. 

In  this  experiment  the  chlorin  decomposes  the  water 
by  taking  out  its  hydrogen  and  setting  the  oxygen  free. 
The  oxygen,  at  the  moment  it  is  set  free,  has  a  strong 
action  on  the  coloring  matter  of  the  cloth  and  destroys 
it.  The  color  may  all  be  taken  out  without  injuring  the 
cloth,  provided  the  cloth  is  removed  from  the  gas  as 
soon  as  the  color  is  gone. 

Bleaching  powder.  Chlorin  is  manufactured  in  very 
large  amounts  for  the  making  of  bleaching  powder. 
In  making  the  bleaching  powder,  lime  is  spread  in 
thin  layers  on  the  floor  of  stone  chambers  and 
chlorin  is  passed  in. 
The  .lime  is  turned 
over  at  intervals  un- 
til it  is  thoroughly 
saturated  with  the 
chlorin.  When  this 
compound  is  placed  in 
water,  the  chlorin  is 
given  off  and  bleaches 
out  the  color  from  cloth 
which  is  immersed  in 

it.  carbon   free. 


86 


Science  for  Beginners 


FIG.  58.     The  sodium  combines  with  the 


Chlorin  as  a  disinfect- 
ant. Chlorin  is  one  of  the 
most  powerful  disinfect- 
ants* known,  and  both 
chlorin  itself  and  com- 
pounds of  it  are  used  to 
make  safe  water  that  may 
contain  disease  germs. 
The  chlorin  kills  germs  in 
the  same  way  that  it 


water  and  releases  the  hydrogen,  which     bleaches    cloth,  -  by 


**  *  composing  the  water  and 

setting   free  the  oxygen, 

which  burns  up  the  germs.  Seventeen  parts  of  chlorin 
in  a  million  parts  of  water  will  destroy  all  germ  life; 
and  since  the  chlorin  does  not  remain  in  a  free  form,  the 
taste  and  drinking  qualities  of  the  water  are  not  impaired. 
By  dragging  a  bag  of  bleaching  powder  back  and  forth 
through  a  swimming  pool,  the  water  of  the  pool  may  be 
freed  from  germs.  The  bleaching  powder  must  be  fresh 
to  be  effective,  and  should  be  applied  in  the  proportion 
of  2  to  10  ounces  to  50,000  gallons  of  water. 

Sodium.  Sodium  belongs  to  a  class  of  rare  metals, 
of  which  sodium  and  potassium  are  the  best  known. 
They  differ  from  iron,  silver,  and  other  metals  with 
which  you  are  more  familiar  in  that  they  are  very  soft 
and  light  —  soft  enough  to  be  easily  cut  with  a  knife, 
and  so  light  that  they  float  on  the  surface  of  water. 
The  cut  surface  of  sodium  shines  with  the  brilliancy  of 
a  piece  of  polished  silver.  In  their  pure  form  these 


Chlorin  and  Sodium  87 

metals  are  used  only  by  the  chemist,  but  compounds 
of  them  are  very  abundant  and  most  valuable.  Thus 
sodium  chlorid,  or  common  salt,  is,  as  we  have  learned, 
found  everywhere,  in  the  sea  and  in  the  soil,  and  some- 
times in  thick  beds  from  which  it  may  be  mined. 
Sodium  carbonate,  a  compound  of  sodium,  carbon,  and 
oxygen,  is  used  in  enormous  quantities  in  cooking,  glass 
making,  and  other  industries.  Perhaps  you  are  familiar 
with  this  compound  under  the  name  of  "  sal  soda"  or 
"baking  soda." 

Strange  metals.  Sodium  and  potassium  have  so 
strong  an  attraction  for  oxygen  that  they  take  the  oxygeji 
of  water  away  from  the  hydrogen,  thus  decomposing  the 
water  and  releasing  the  hydrogen  as  a  free  gas.  The 
following  experiments  will  illustrate  this  most  remarkable 
property. 

Exercise  5.  Into  a  beaker  glass  or  tumbler  one  third 
full  of  water  drop  a  small  piece  of  potassium.  Stand  away 
from  it  until  the  very  vigorous  action  ceases.  If  sodium  is 
used,  the  water  should  be  slightly  warm. 

The  metals  float  on  the  surface  of  the  water ;  they 
move  about  very  rapidly  and  the  hydrogen  which  is 
given  off  is  set  on  fire  by  the  heat  from  the  chemical 
action.  The  color  of  the  flame  is  given  to  it  by  the 
metal.  If  sodium  is  used,  it  is  tinged  with  yellow,  or 
with  a  bright  violet  color  if  potassium  is  used. 

Exercise  6.  Make  a  small,  deep  cavity  in  a  piece  of  ice 
and  drop  into  it  a  small  piece  of  potassium.  Immediately 
a  flame  appears,  tinged  with  a  purple  color,  as  if  the  ice 
had  been  set  on  fire.  A  sharp  explosion  usually  ends  the 


88 


Science  for  Beginners 


experiment.     The  flame   is  produced   by  the  burning  of 
hydrogen  which  has  been  pushed  out  of  the  water  molecules 

by  the  potassium  (Fig.  59). 
Exercise  7.  Fill  a  test 
tube  with  water  and  invert 
it  in  a  dish  of  water.  Wrap 
a  small  piece  of  sodium 
loosely  in  a  piece  of  paper, 
and  with  a  pair  of  forceps 
(not  with  the  fingers)  hold 
it  under  the  inverted  test 
tube.  A  gas  is  given  off, 
partly  filling  the  test  tube. 
Carefully  lift  the  tube  con- 
taining the  gas  out  of  the 
water,  keeping  the  mouth 
down,  and  bring  its  mouth 

to  the  flame  of  a  lam? or 

Bunsen  burner.  A  slight 
explosion  shows  the  gas  to  be  hydrogen. 

Exercise  8.  Take  a  dish  partly  full  of  pure,  distilled 
water.  Add  two  small  pieces  of  litmus  paper,  one  blue  and 
the  other  red.  Does  the  water  make  any  change  in  the 
color  of  either  of  the  papers?  Water  is  said  to  be  neutral* 
to  litmus ;  it  does  not  change  its  color. 

Exercise  9.  Place  red  litmus  paper  in  water  on  which 
sodium  or  potassium  has  acted.  It  turns  blue,  showing 
that  a  new  substance  has  been  produced  in  the  water.  It 
is  plain  that  the  new  substance  is  not  an  acid  but  an  alkali. 

Cautiously  taste  the  solution.  Touch  your  finger  to  it. 
Notice  the  "  soapy  feel."  Some  new  compound  has  been 
formed  by  the  sodium  and  the  water. 


FIG.  59. 


Chlorin  and  Sodium  89 

The  story  of  what  has  happened  is  as  follows : 
H2O  +  Na  ->     H    +    NaOH 

water    +  sodium  — >  hydrogen  +  sodium  hydroxid 

The  sodium  has  displaced  one  of  the  hydrogen  atoms 
in  the  molecule  of  water,  making  a  new  substance, 
sodium  hydroxid  (NaOH).  This  new  substance  is 
commonly  called  caustic  soda,  and  it  belongs  to  a  class 
of  compounds  known  as  bases. 

Bases.  In  the  chapter  on  hydrogen  you  studied 
about  acids  and  tested  certain  substances  for  acidity* 
with  litmus  paper.  Some  substances  turned  the  litmus 
paper  red ;  other  substances  made  the  blue  color  more 
intense,  or,  if  a  red  paper  were  used,  turned  it  blue.  These 
latter  substances  are  known  as  bases,  and  they  are 
alkaline*  to  the  litmus  paper.  The  best  examples  of 
bases  are  what  are  commonly  called  "  potash  "  and 
"  soda."  Other  examples  are  baking  soda  and  lime. 

Properties  of  a  base.  Three  properties  which  may 
be  used  to  distinguish  a  base  are : 

(1)  It  is  caustic  or  burning  to  the  taste. 

(2)  It  will  turn  red  litmus  paper  blue. 

(3)  It  always   contains   a   metal   with   oxygen   and 
hydrogen. 

Compare  these  properties  with  the  corresponding 
properties  of  acids  (page  58) . 

Acids  and  bases  neutralize  each  other.  Another 
experiment  will  give  an  interesting  illustration  of  the 
behavior  of  a  base. 

Exercise  10.  In  a  weak  solution  of  hydrochloric  acid 
place  a  small  piece  of  litmus  paper.  What  color  is  produced  ? 


po  Science  for  Beginners 

Are  you  dealing  with  an  acid  or  a  base?  Now  add  slowly 
a  weak  solution  of  caustic  soda  (sodium  hydroxid).  Stir 
the  mixture  thoroughly  and  continue  to  add  the  acid  until 
the  litmus  is  turned  to  a  very  faint  blue  color.  Save  the 
solution  for  use  in  the  next  experiment. 

In  this  experiment  the  base  has  destroyed,  or  neu- 
tralized, the  acid;  or,  rather,  the  acid  and  the  base 
neutralized  each  other.  After  the  acid  was  all  used  up, 
the  solution  became  alkaline  and  the  litmus  turned 
blue.  Whenever  acids  and  bases  are  brought  together 
they  neutralize,  or  destroy,  each  other  in  this  way. 

Some  practical  uses  of  a  chemical  principle.  The 
busy  bee  extracts  the  sweets  from  the  flowers  and  for 
the  most  part  deposits  them  in  his  curiously  constructed 
comb  as  honey.  A  part  of  the  sugar,  however,  is  changed 
in  the  body  of  the  bee  to  an  acid  known  as  formic  acid, 
and  when  the  bee  stings  us  we  get  the  benefit  of  this 
acid.  To  allay  the  poison  of  the  sting  we  apply  ammo- 
nia or  baking  soda  to  the  wound.  These  are  bases,  and 
their  healing  power  lies  in  their  ability  to  neutralize 
the  acid  of  the  sting.  We  neutralize  the  acid  of  sour 
milk  by  the  use  of  baking  soda;  the  thrifty  housewife 
saves  her  sugar  by  dusting  soda  over  a  rhubarb,  goose- 
berry, or  cherry  pie ;  and  the  farmer  "  sweetens  "  his 
soil  by  treating  it  with  lime.  In  all  these  cases  a  base 
is  being  used  to  destroy  the  sour  acid  which  injures  or 
offends  us. 

Salts.  When  an  acid  and  a  base  neutralize  each  other, 
they  do  not  cease  to  exist.  What  becomes  of  them? 
A  continuation  of  our  last  experiment  will  give  us  light. 


Chlorin  and  Sodium  91 

Exercise  n.  Place  the  solution  from  the  last  experiment 
in  an  evaporating  dish  and  heat  it  to  drive  off  the  water. 
The  dry  substance  which  remains  is  common  salt.  Taste 
it  to  learn  that  it  is  salt. 

Common  salt  is  only  one  of  a  great  number  of 
compounds  which  chemists  call  salts.  Whenever  an 
acid  and  a  base  neutralize  each  other,  a  salt  is  formed. 
There  are  hundreds  of  different  kinds  of  salts,  and  when 
the  chemist  uses  the  word  "  salt  "  he  does  not  mean  by 
it  the  one  substance  which  we  commonly  know  as  salt. 

What  happens  when  an  acid  and  a  base  act  on  each 
other.  What  really  took  place  in  Exercise  10  was  the 
following : 

NaOH    +       HC1        ->        NaCl   +  H2O 

sodium  hydroxid  +  hydrochloric  acid     — ^      sodium  chlorid  +  water 

The  sodium  of  the  base  changed  places  with  the  hydro- 
gen  of  the  acid.  Study  out  the  full  meaning  of  this 
statement  and  see  if  it  is  clear  to  you  that  in  the  above 
chemical  reaction  common  salt  and  water  would  be 
formed.  Whenever  an  acid  and  a  base  act  on  each  other, 
they  exchange  or  trade  atoms.  The  acid  gives  the  base 
its  hydrogen  and  receives  in  exchange  a  metal. 

This  kind  of  chemical  action  is  known  as  neutraliza- 
tion. It  takes  place  whenever  a  base  and  an  acid  are 
brought  together.  One  product  of  the  process  is  al- 
ways water,  and  the  other  product  is  a  salt.  Salts  are 
much  more  numerous  in  nature  than  acids  or  bases  be- 
cause of  the  fact  that  when  an  acid  is  produced  there 
is  likely  to  be  some  base  present  which  will  neutralize  it 
into  a  salt. 


CHAPTER  ELEVEN 


A  STUDY  OF  A  MATCH 


SULFUR   AND   PHOSPHORUS 


FIG.  ,60.    One  way  of  carrying  fire. 


IN  these  days  of  Welsbach 
burners  and  Mazda  lamps, 
it  will  be  interesting  to  get 
from  Grandmother  the  story 
of  the  tinder  box  and  the  flint 
and  steel  as  a  means  of  ob- 
taining fire;  or  of  how,  fail- 
ing to  get  the  fire  in  this  way, 
the  housekeeper  borrowed  a 
pan  of  live  coals  from  a  neigh- 
bor's kitchen;  or,  perhaps, 
carried  the  fire  home  upon  a 
stick  which  was  kept  alive  and 
glowing  by  waving  it  back 
and  forth  in  the  air.  In  olden 
times,  fires  were  not  allowed 


to  go  out,  for  the  reason  that 
there  were  no  matches  to  light  them  again.  Let  us  study 
in  this  chapter  the  convenient  little  article  that  now 
makes  it  possible  for  us  to  have  fire  and  light  at  any 
time. 

The  first  matches.  Early  in  the  nineteenth  century  it 
was  discovered  that  potassium  chlorate  mixed  with  sugar 
would  burst  into  flame  when  acted  upon  by  sulfuric  acid. 
Following  this  discovery  an  inventive  genius  placed  upon 
the  market  a  box  containing  one  hundred  splints  of  wood 
previously  soaked  in  a  solution  of  potassium  chlorate  and 

92 


A  Study  of  a  Match 


93 


sugar,  and  a  little  vial 
holding  asbestos*  satu- 
rated with  sulfuric  acid. 
For  the  hundred 
matches  and  the  vial 
of  acid  he  charged  a 
guinea*,  and  only  the 
well-to-do  could  afford 
them.  The  result  of 
bringing  together  the 
chemicals  that  were 
used  in  these  first 
matches  may  be  seen 
in  the  following  ex- 
periment : 

Exercise  i.  In  a  clean 
porcelain  mortar,  pulver- 
ize a  small  amount  of  po- 
tassium chlorate  (KC1O3)  to  a  fine  powder.  In  doing  this, 
care. must  be  taken  to  see  that  the  pestle  and  mortar  are 
perfectly  clean  and  free  from  organic  matter  and  that  the 
potassium  chlorate  is  free  from  dust.  Avoid  violent  percus- 
sion* or  heavy  pressure  upon  the  contents  of  the  mortar. 
Place  the  powder  on  a  piece  of  paper  and  add  an  equal 
bulk  of  granulated  sugar  (C^H^On)  which  has  previously 
been  dried  and  powdered.  Mix  the  two  materials  together 
carefully,  without  rubbing  them,  as  the  mixture  is  likely  to  ex- 
plode if  strongly  rubbed .  Place  the  mixture  on  a  brick  or  stone 
out  of  doors  or  in  a  strong  draft  of  air.  Let  fall  upon  the 
mixture  a  drop  of  sulfuric  acid  from  the  end  of  a  glass  rod. 
A  very  quick  chemical  action  will  follow,  with  a  violet-colored 


FIG.  61.    An  experiment  to  show  how  fire 
may  be  kindled  by  chemical  action. 


94 


Science  for  Beginners 


National  Match  Company 
FIG.  62.    Unloading  basswood  logs  at  a  match  factory. 

flame.    The  color  of  the  flame  is  due  to  the  vaporization*  of 
the  metal  potassium  contained  in  the  potassium  chlorate. 

The  friction  match.  The  friction  match  was  invented 
in  1827  by  John  Walker,  an  English  chemist.  He  used 
a  mixture  of  antimony  sulfid  (Sb2S3)  and  potassium 
chlorate  (KClOs)  on  the  end  of  a  splinter  of  wood.  This 
had  to  be  rubbed  between  two  pieces  of  sandpaper. 
Afterwards,  phosphorus  was  substituted  for  the  anti- 
mony compound  and  sulfur  for  the  potassium  chlorate. 
These  and  other  chemicals  are  used  to  produce  the  dif- 
ferent kinds  of  matches  now  found  upon  the  market. 

What  is  needed  for  the  end  of  a  friction  match  is  a 
substance  that  will  take  fire  easily,  and  the  chemist  can 
supply  a  number  of  combinations  of  chemicals  that  will 
do  this.  The  matchmaker  then  mixes  these  chemicals 
with  clay,  whiting,  starch,  gum,  rosin,  lampblack  or  a 


A  Study  of  a  Match 


95 


dye,  glue,  and  other  materials,  dips  the  ends  of  pine  or 
basswood  splints  into  the  mixture,  and  sells  the  results  of 
his  labor  in  the  form  of 
the  modern  match. 

Two  varieties  of  the 
friction  match.  Two 
varieties  of  the  friction 
match  are  in  common 
use  :  the  strike-any- 
where match  and  the 
strike-on-box  kind.  In 
making  the  strike-any- 
where match,  about  half 
an  inch  of  the  stick  is 
first  soaked  in  melted 
paraffin  or  sulfur.  Then 
the  head  is  coated  with 
some  easily  combusti- 
ble chemical  mixture 
to  which  fine  sand  or 
powdered  glass  has  been 
added  to  keep  the  head 
porous  and  thus  allow 
the  en  trance  of  air.  Lead 
oxid  and  phosphorus,  or 
potassium  chlorate  and 
phosphorus,  are  the 
chemicals  often  em- 
ployed in  making 
matches  of  this  kind. 


J\ anonal  Match  Company 
FIG.  63.  Scene  in  a  match  factory.  600 
match  sticks  are  punched  by  machinery 
into  holes  in  each  of  the  plates,  which  form 
the  sections  of  the  great  belt  shown  in  the 
illustration.  The  belt  passes  over  the  dip- 
ping kettles,  where  the  tips  of  the  sticks 
pass  through  the  chemicals,  after  which  the 
matches  are  carried  over  the  wheels  until 
dry.  They  are  then  punched  out  of  the 
plates  and  fed  automatically  into  boxes. 
One  machine  will  turn  out  6,ooo,oo<? 
matches  in  10  hours. 


g6  Science  for  Beginners 

The  strike-on-box  match  differs  from  the  strike-any- 
where variety  in  that  part  of  the  chemicals  are  on  the 
match  and  part  on  the  box.  Such  matches  can  be 
easily  ignited  only  by  friction  of  the  match  on  the  box, 
and  are  therefore  called  "  safety  "  matches.  But  ex- 
perience with  them  shows  that  they  are  open  to  some 
serious  objections.  Usually  the  splints  are  smaller  and 
thinner  than  the  sticks  of  the  ordinary  match  and  the 
wood  is  of  inferior  quality.  They  break  easily  and 
there  is  danger  that  a  blazing  match  head  may  fly  into 
inflammable  materials. 

Determining  the  presence  of  phosphorus  and  sulfur 
in  matches.  You  will  not  be  able  to  determine  all  the 
chemicals  used  in  making  a  match,  but  by  experiment 
you  can  learn  to  recognize  the  presence  of  two  elements, 
phosphorus  and  sulfur,  that  are  very  commonly  used. 

Exercise  2.  Strike  different  kinds  of  matches,  and  ob- 
serve them  closely  as  they  burn.  Some  of  them  will  give 
off  a  little  cloud  of  smoke  immediately  after  the  match  is 
lighted.  In  some  cases  a  bluish  flame  will  be  seen,  or,  if  the 
match  is  held  close  to  the  nose,  a  stifling  odor  will  be  de- 
tected. 

To  a  chemist,  the  appearance  of  the  white  cloud 
means  that  the  match  contains  the  element  phosphorus. 
The  cloud  is  composed  of  fine  particles  of  a  white  solid 
which  is  produced  by  the  union  of  the  phosphorus  of 
the  match  with  the  oxygen  of  the  air.  It  is  an  oxid  of 
phosphorus  (P2O5). 

The  blue  flame  which  follows  the  white  cloud  suggests 
sulfur  to  the  chemist.  He  smells  the  stifling  gas  and  at 


A  Study  of  a  Match  97 

once  recognizes  the  odor  of  sulfur  dioxid  (862),  a  sub- 
stance which  is  formed  when  sulfur  unites  with  oxygen. 

Occurrence  of  phosphorus.  Compounds  of  phos- 
phorus are  found  in  the  yolk  of  egg  and  in  considerable 
amounts  in  nuts,  peas,  wheat,  and  other  vegetable  prod- 
ucts. Calcium  phosphate  (CatfPOJj)  forms  about  25 
per  cent  of  the  bones  of  animals,  and  the  same  compound 
is  scattered  in  soils.  Occasionally  it  is  found  in  great 
deposits  as  a  mineral  called  rock  phosphate.  Very 
valuable  phosphate  deposits  are  found  in  South  Carolina 
and  Tennessee. 

Uses  of  phosphorus.  This  element  is  necessary  to 
the  growth  of  vegetable  products,  and  these,  in  turn,  when 
used  as  food  by  man  and  other  animals,  supply  the  needed 
phosphorus  to  the  bones  and  muscles,  nerves  and  brain. 
Hence  it  is  that  rocks  containing  phosphorus  are  neces- 
sary and  valuable  ingredients  in  fertilizers*  used  to  enrich 
the  soil.  The  most  extensive  known  deposits  of  phos- 
phate rocks  are  in  our  own  country.  These  rocks  are 
mined  and  shipped  for  fertilizers  to  the  different  coun- 
tries of  Europe. 

Manufacture  of  phosphorus.  Phosphorus  is  manu- 
factured from  natural  calcium  phosphate  by  mixing  it 
with  sand  (Si02)  and  coke  and  heating  the  mixture  in 
an  electric  furnace.  The  phosphorus  separates  as  a 
vapor  and  is  condensed  to  a  solid' under  water.  White 
phosphorus  will  ignite  and  burn  furiously  if  left  exposed 
to  the  air  and  for  this  reason  is  kept  under  water.  It 
should  never  be  touched  with  the  hands,  as  it  may  stick 
to  the  fingers  and  cause  very  severe  burns.  It  is  very 


98  Science  for  Beginners 

poisonous,  and  phosphorus  matches  should  not  be  left 
where  young  children  can  reach  them. 

Occurrence  of  sulfur.  Formerly  sulfur  was  obtained 
from  the  deposits  to  be  found  in  volcanic  regions.  Under 
the  action  of  the  heat  of  the  volcano  the  sulfur  was 
separated  from  its  compounds  and  brought  to  the  sur- 
face. By  melting  the  sulfur  away  from  the  impurities 
a  comparatively  pure  product  was  obtained.  Sulfur 
produced  in  this  way  was  shipped  from  Sicily  and  Ice- 
land to  all  parts  of  the  world.  More  recently  enormous 
deposits  of  nearly  pure  sulfur  have  been  discovered  in 
Louisiana ;  and  although  the  material  is  solid  and  cov- 
ered with  900  feet  of  quicksand,  clay,  and  rock,  it  is 
lifted  to  the  surface.  The  ingenious  method  by  which 
this  is  done  is  one  of  the  engineering  triumphs  of  our 
age.1 

Uses  of  sulfur.  Sulfuric  acid  (H2S04),  the  most  im- 
portant single  chemical  that  could  be  named,  is  made 
from  sulfur.  Sulfur  dioxid,  which  is  produced  by  burn- 
ing sulfur,  is  used  in  bleaching  feathers,  straw,  and  wool 
and  in  paper  making.  Pure  sulfur  is  used  in  making 
gunpowder,  matches,  and  fireworks,  and  in  the  vul- 
canizing* of  rubber.  Farmers  and  the  owners  of  or- 
chards and  vineyards  make  much  use  of  sulfur  compounds 

1  Borings  are  made  and  in  each  boring  4  pipes  are  extended  downward 
to  the  sulfur  bed.  The  pipes  have  diameters  of  8  inches,  6  inches,  3 
inches,  and  i  inch  respectively,  and  the  smaller  pipes  are  placed  inside 
the  larger.  Water  heated  to  170  degrees  Fahrenheit  is  pumped  down 
the  2  larger  pipes,  which  melts  the  sulfur.  Compressed  air  is  then  forced 
down  the  i-inch  pipe  and  this  causes  the  liquid  sulfur  to  rise  through  the 
3-inch  pipe. 


A  Study  of  a  Match  99 

as  a  spray  to  destroy  the  parasites*  that  otherwise  would 
blast  the  apples  and  other  fruits. 

The  meaning  of  "ate"  in  chemical  names.  In  this 
chapter  we  have  used  a  number  of  chemical  names 
that  end  in  "  ate,"  —  potassium  chlorate,  potassium 
nitrate,  and  calcium  phosphate.  When  the  name  of  a 
chemical  compound  ends  in  "  ate,"  the  substance  con- 
tains oxygen  in  addition  to  the  elements  mentioned  in 
the  name.  Thus,  potassium  chlorate  contains  potas- 
sium, chlorin,  and  oxygen ;  calcium  phosphate  is  made 
up  of  calcium,  phosphorus,  and  oxygen ;  silver  nitrate 
contains  silver,  nitrogen,  and  oxygen;  calcium  carbon- 
ate, or  limestone,  contains  calcium,  carbon,  and  oxygen. 

Matches  and  fires.  Most  fires  are  caused  by  the  care- 
less throwing  away  of  lighted  matches.  An  experiment 
will  show  how  the  match  manufacturer  is  lessening  the 
danger  of  fire  from  this  source. 

Exercise  3.  Ignite  splinters  of  dry  pine  or  basswood. 
Blow  them  out  and  note  if  the  wood  continues  to  glow 
after  the  flame  has  been  extinguished. 

In  the  same  way  test  matches  of  several  different  kinds. 
Does  the  wood  of  some  of  them  cease  to  burn  as  soon  as' 
the  flame  is  blown  out  ? 

The  wood  of  matches  is  now  often  "  fireproof ed  "  by 
impregnating*  it  with  certain  chemicals.  Sodium  phos- 
phate or  alum  may  be  used  for  this  purpose. 


CHAPTER  TWELVE 


CARBON  AND  ITS  COMPOUNDS 

IN  a  former  chapter  we  learned  that  oxygen  is  the 
most  abundant  element  in  the  crust  of  the  earth  and 
therefore  the  greatest  in  amount  in  the  soil.  If  we  turn 
our  attention  to  the  things  that  live  and  grow  in  this 
soil,  we  shall  find  that  in  them  by  far  the  most  abundant 
element  is  carbon. 

Carbon  is  extremely  important,  because  it  is  the  prin- 
cipal element  in  all  organic*  substances ;  that  is,  in  all 

things  which  have  been 
produced  through  the 
agency  of  life.  This 
will  include  all  forms  of 
animal  and  vegetable  life, 
all  animals  and  plants. 
Chemically  considered, 
a  blade  of  grass,  a  rose,  a 
potato,  an  ox,  and  a  man 
differ  but  little  ;  all  of 

FIG.  64.    A  hod  of  carbon.  them  ^^  &  ^  p^_ 

centage  of  carbon  combined  with  hydrogen,  oxygen,  and 
nitrogen,  with  small  amounts  of  phosphorus,  sulfur,  and 
a  few  other  elements.  Carbon  is  the  chief  element  in 
our  foods,  in  wood,  coal,  straw,  feathers,  hair,  leather,  — 
in  everything,  in  fact,  that  is  formed  by  animals  and 
plants.  £very  molecule  of  all  these  compounds  has 
one  or  more  atoms  of  carbon  as  its  center,  and  it  is  this 
remarkable  element  that  we  are  about  to  study. 

Carbon  is  also  to  be  found  in  the  vast  beds  of  lime- 


100 


Carbon  and  Its  Compounds  T.OI 

stone  occurring  in  all  parts  of  the  world,  and  in  the  air 
it  exists  in  the  form  of  the  gas,  carbon  dioxid. 

Exercise  i.  Fill  an  ignition  tube,  provided  with  a  de- 
livery tube  of  glass,  with  shavings  or  small  pieces  of  soft  wood, 
and  heat  it  in  the  flame  of  a  lamp  or  Bunsen  burner.  A 
mixture  of  a  number  of  gases  composed  of  carbon,  hydrogen, 
and  oxygen  will  be  given  off.  Light  the  gas  at  the  end  of 
the  delivery  tube. 

After  the  flow  of  the  gas  has  ceased,  put  a  solid  cork  in  the 
open  end  of  the  test  tube  so  that  no  air  can  enter,  and  let 
the  apparatus  stand  until  it  is  cold. 

The  contents  of  the  tube  will  be  found  to  be  that 
form  of  carbon  known  as  charcoal.  The  gas  given  off 
is  an  impure  illuminating  gas,  which  burns  rather  inter- 
mittently* if  lighted  at  the  end  of  the  pointed,  drawn- 
out  end  of  the  glass  delivery  tube. 

Exercise  2.  Examine  the  charcoal  and  make  a  list  of  its 
properties.  Is  it  solid,  liquid,  or  gaseous?  It  is  an  inter- 
esting fact  that  you  probably  never  will  see  pure,  elemental 
carbon  in  the  liquid  or  gaseous  condition.  Is  it  soluble  in 
water?  Has  it  a  taste?  Has  it  an  odor?  Heat  a  portion 
of  it  and  observe  that  it  glows  but  does  not  burn  with  a 
flame. 

Charcoal  burns  slowly  and  without  smoke;  hence 
it  is  used  for  many  purposes  where  continued  heat  is 
required.  The  plumber  or  tinner  will  carry  his  char- 
coal fire  to  the  top  of  a  building  where  he  is  at  work. 

The  manufacture  of  charcoal.  Charcoal  is  made  on 
a  large  scale  by  piling  logs  of  wood  in  a  large  mound 
or  heap  around  a  central  aperture,*  which  serves  as  a 


i« 


Science  for  Beginners 


FIG.  65.    A  charcoal  kiln. 

chimney.  The  heap  is  covered  with  sods  and  earth, 
or  a  kiln*  of  brick  is  built  around  it ;  but  in  either  case 
a  number  of  openings  are  left  for  the  admission  of  air. 
A  fire  is  built  at  the  center  and  the  whole  mass  slowly 
burned  for  several  days.  The  chemical  action  here  is 
exactly  the  same  as  that  which  took  place  in  the  ignition 
tube :  the  hydrogen  and  oxygen  of  the  wood,  combined 
with  a  certain  amount  of  carbon,  are  driven  off  as  gases. 
The  remaining  carbon  is  left  behind  as  charcoal.  This 
forms  about  65  or  70  per  cent  of  the  bulk  of  the  wood  and 
four  tenths  of  its  weight. 

Exercise  3.  Put  into  an  ignition  tube  enough  soft  coal 
to  fill  one  third  of  the  tube.  Heat  the  coal  and  collect  in 
bottles  the  gas  which  comes  off.  Light  the  gas  at  the  end  of 
the  delivery  tube.  It  will  burn  with  a  yellow  flame.  This 
also  is  an  impure  illuminating  gas. 

Coke.  As  soon  as  gas  ceases  to  be  given  off  and  the 
tube  has  cooled,  break  the  tube  and  examine  the  black 
solid  which  it  contains.  This  solid  is  coke,  a  form  of 
carbon  which  is  practically  the  same  as  charcoal,  but 
usually  more  solid  and  compact.  Coke  making  is  a 
great  industry,  and  large  quantities  of  illuminating  gas 


Carbon  and  Its  Compounds  103 

are  secured  from  the  coal  that  is  heated  in  this  process. 
Procure  samples  of  coke  from  a  coal  yard  and  examine 
them  thoroughly.  Charcoal  and  coke  are  used  very 
extensively  as  agents  for  the  reduction  of  the  ores  of 
iron,  copper,  lead,  tin,  and  other  metals.  What  that 
statement  means  can  be  understood  by  a  single  illus- 
tration. 

Iron  ore  is  iron  oxid,  a  compound  of  iron  and  oxygen. 
When  this  ore  is  mixed  with  coke  or  charcoal  and  heated 
to  a  high  temperature,  the  carbon  unites  very  vigorously 
with  the  oxygen  of  the  ore  and  leaves  the  metal  in  the 
free  state. 

In  other  words,  the  coke  takes  the  oxygen  away  from 
the  iron,  leaving  the  iron  atoms  behind  to  combine  with 
each  other  and  form  molecules  of  iron.  This  process 
of  taking  oxygen  away  from  a  substance  is  called  by  the 
chemist  reduction.  It  is  the  opposite  of  oxidation. 
What  is  oxidation? 

Fe203  +  3C    ->    2Fe+      3  CO 

iron  ore    +    coke      — >•       iron      +  carbon  monoxid* 

Lampblack,  or  soot.  This  is  finely  divided  charcoal. 
In  performing  the  experiments  described  on  pages  55 
and  84  you  have  already  produced  it,  and  small  amounts 
of  it  can  be  secured  in  a  still  simpler  way. 

Exercise  4.  Press  down  an  iron  spoon  or  porcelain  plate 
upon  the  flame  of  an  oil  lamp  or  candle.  Carbon  is  deposited 
on  the  spoon  or  plate.  Where  does  it  come  from  ? 

The  explanation  of  this  experiment  is  that  the  tem- 
perature of  the  flame  is  lowered  below  the  burning  point 
of  the  carbon. 


IO4 


Science  for  Beginners 


How  lampblack  is  manu- 
factured. Lampblack  is 
manufactured  commercially 
from  tar,  crude  petroleum, 
resin,  or  pine  knots  that  are 
rich  in  resin  and  turpentine. 
The  process  is  as  follows: 
The  carbon-containing  sub- 
stance is  heated  in  a  vessel, 
and  the  vapors  from  it  are 
driven  into  a  chamber  in 
which  there  is  a  scant  supply 
of  air.  A  dense  cloud  of 
unburned  carbon  particles 
enters  the  chamber  and  col- 
lects on  canvas  hung  on  the 
walls  of  the  chamber.  This 
deposit  is  scraped  from  the 
walls  at  suitable  intervals  by 
lowering  a  hood. 

The  lampblack  so  produced  contains  many  impurities, 
such  as  oils  and  tars.  It  is  separated  from  these  by 
heating  to  redness.  The  principal  use  of  lampblack  is 
in  the  manufacture  of  printing  inks.  It  is  also  used  for 
the  production  of  India  ink  and  for  a  cheap  black  paint. 
Graphite.  Graphite*  is  a  second  form  of  carbon. 
It  is  found  in  certain  parts  of  the  world  in  the  form  of 
a  mineral.  It  is  always  opaque,*  of  a  black  or  lead-gray 
color,  and  of  a  metallic  luster.*  The  most  familiar 
use  of  graphite  is  in  the  so-called  "  lead  "  pencils.  The 


.  00.     Collecting  lampblack. 


Carbon  and  Its  Compounds 


105 


finely  ground  graphite  is  mixed  with  clay  to  give  the 
required  hardness  and  is  then  molded  in  the  form  seen 
in  the  pencil.  It  is  also  used  in  common  stove  polishes, 
in  the  manufacture  of  crucibles*  for  use  in  the  chemical 
laboratory,  and  as  a  lubricant  for  the  chains  of  bicycles, 
the  cylinders  of  gasoline 
engines,  and  the  bear- 
ings of  other  machines. 
The  diamond.  A  third 
form  of  carbon  is  the 
diamond.  Stories  of 
some  of  the  noted  dia- 
monds of  the  world  may 
be  found  in  the  ency- 
clopedia* or  other  books 
of  reference.  The  im- 
agination* must  be  used  '  •'  "•  '•' ; ; '' 

.  .     .  FIG.  67.    Manufacturing  lampblack. 

to  picture  to  the  mind 

their  wonderful  brilliancy.  The  diamond  is  usually 
considered  the  most  precious  of  gems,  but  the  ruby,  the 
emerald,  and  the  sapphire  are  close  rivals  in  beauty 
and  value.1  The  diamond  is  noted  for  its  wonderful 
power  to  refract  the  light,  sending  it  forth  to  dazzle  the 

1  It  will  be  interesting  to  note  the  comparatively  simple  chemical 
composition  of  some  of  the  precious  stones  and  gems  of  jewelry. 

The  diamond  is  pure  carbon,  C. 

The  ruby  is  the  oxid  of  aluminium,  A12O3,  made  red  by  a  small  trace 
of  chromium. 

The  sapphire  also  is  an  oxid  of  aluminium,  Al2Oa,  made  blue  by  a  small 
trace  of  iron  or  titanium. 

The  emerald  is  a  complex  compound  of  glucinum,  aluminium,  silicon, 
chromium,  and  oxygen,—  Gl3Al2(SiO3)6  +  a  trace  of  CrSiO3. 


io6 


Science  for  Beginners 


FIG.  68.    Crystals  of  carbon. 

eye  with  its  beauty.  Diamonds  are  found  chiefly  in 
South  Africa  and  Brazil.  When  first  found  they  are 
incrusted  over  with  the  rock  in  which  they  have  crys- 
tallized, and  it  takes  the  practiced  eye  of  an  expert 
miner  to  detect  them.  They  are  perfect  crystals  when 
found,  but  usually  they  are  put  into  the  hands  of  a  dia- 
mond cutter,  who  grinds  new  and  additional  faces  to  in- 
crease their  brilliancy. 

Composition  of  the  diamond.  As  chemists,  what 
we  are  most  interested  in  knowing  about  the  dia- 
mond is  its  composition.  When  ordinary  charcoal 
is  burned  in  pure  oxygen,  carbon  dioxid  is  produced; 
and  when  the  diamond  is  burned  in  pure  oxygen, 
carbon  dioxid  is  again  produced.  In  both  cases  the 
chemical  reaction  is: 

C  +  02  ->  C02 

We  cannot,  therefore,  escape  the  conclusion  that 
the  diamond  has  the  same  chemical  composition  as 
ordinary  charcoal.  The  difference  between  them  is 
simply  a  matter  of  crystallization.  Diamonds  have 


Carbon  and  Its  Compounds 


107 


been  produced  in  the  laboratory  by  subjecting  pure 
carbon  to  intense  heat  under  high  pressure.  But  the 
process  is  very  expensive,  and  only  small  diamonds  have 
been  made  in  this  way. 

Carbon  dioxid.  The  fact  has  already  been  stated 
that  when  carbon  is  burned  in  the  air,  a  gas  is 
given  off.  This  is  the  gas  known  as  carbon  dioxid. 
Notice  how  appropriate  the  name  is,  since  the  gas  is 
formed  from  carbon  and  oxygen  and,  as  is  shown  by 
the  prefix*  di,  contains  two  parts  of  oxygen  to  one  of 
carbon.  The  chemist  writes  the  formula  for  this  gas 

CO2. 

Occurrence  of  carbon  dioxid.  Carbon  dioxid  is  formed 
whenever  any  organic  substance  is  acted  upon  by 
the  oxygen  of  the  air.  Thus,  if  a  piece  of  wood  falls 
to  the  ground  and  de- 
cays, carbon  dioxid  is 
formed.  If  a  similar 
piece  of  wood  is  burned 
in  .the  stove,  carbon 
dioxid  is  produced  and 
goes  up  the  chimney. 
It  can  be  found  in  the 
gases  which  escape  from 
a  burning  candle,  lamp, 
or  gas  jet ;  and  in  the 
same  way  it  may  be 
found  in  the  breath 
which  is  thrown  off  from 

the  lungs.  FIG.  69.    Collecting  carbon  dioxid. 


io8 


Science  for  Beginners 


FIG.  70.    The  candle  flame  goes  out 
when  carbon  dioxid  is  poured  over  it. 


In  order  to  become  better 
acquainted  with  this  gas, 
we  shall  manufacture  it  and 
learn  some  of  its  properties. 
Exercise  5.  Put  into  a 
bottle,  arranged  as  shown  in 
Figure  69,  small  pieces  of 
marble  or  limestone.  Pour 
dilute  hydrochloric  acid  into 
the  bottle  through  the  thistle 
tube.  Carbon  dioxid  is 
evolved  at  once  and  may  be 
collected  over  water  or  by 
downward  displacement  of 
air  (Fig.  69). 

Exercise  6.  Upon  a  candle  burning  at  the  bottom  of  a 
glass  (Fig.  70)  pour  the  carbon  dioxid  collected  in  Exercise  5 
and  note  the  result.  The  same  result  may  be  produced  by 
lowering  the  lighted  taper  into  a  jar  which  is  filled  with  the  gas. 

How  to  test  for  carbon  dioxid.  The  test  which  is 
commonly  used  in  the  laboratory  for  the  detection  of 
carbon  dioxid  is  the  "  limewater  test."  A  saturated 
solution  of  fresh  quicklime  is  prepared  by  pulverizing 
the  lime  and  placing  it  in  a  flask  of  pure  water.  The 
flask  is  shaken  frequently  and  allowed  to  stand  until 
the  water  has  dissolved  the  greatest  possible  amount 
of  the  lime.  Then  the  excess  lime  is  allowed  to  settle 
and  the  clear  liquid  is  drawn  off  and  put  into  a  stop- 
pered bottle  for  future  use. 

Exercise  7.  Hold  a  flask  or  test  tube  containing  a  small 
amount  of  limewater  under  the  delivery  tube  of  a  carbon 


Carbon  and  Its  Compounds 


109 


dioxid  generator  (Fig.  69)  in  such  a  way  that  the  gas  escapes 
into  the  water.  A  white  cloud,  or  turbidity,*  appears  in 
the  limewater.  * 

As  will  be  explained  in  a  later  chapter,  this  white 
turbidity  or  precipitate,  as  it  is  properly  called,  has  the 
exact  chemical  composition  of  limestone.  Its  appear- 
ance in  limewater  is  proof  of  the  presence  of  carbon 

dioxid. 

Limewater  +  carbon  dioxid  ->  limestone 

Exercise  8.  Expose  to  the  air  a  small  amount  of  lime- 
water  in  a  saucer  or  watch  glass.  Examine  the  surface  of 
the  limewater.  Is  there  carbon  dioxid  in  the  air? 

Exercise  9.-  Blow  air  into  a  vessel  of  limewater  through  a 
tube  or  straw.  What  is  the 
result?  What  caused  it?  Where 
does  the  carbon  dioxid  in  the 
breath  come  from?  Give  two 
reasons  why  you  breathe. 

Exercise  10.  Make  a  loop 
in  the  end  of  a  piece  of  wire  by 
bending  it  around  a  small  lead 
pencil.  Pass  the  wire  through 
a  piece  of  cardboard  or  stiff 
paper  as  shown  in  Figure  71. 
Insert  the  loop  of  the  wire 
into  clear  limewater;  when  it 
is  taken  out  it  will  hold  a  thin 
film  of  the  water.  Lower  the 
wire  into  a  lamp  chimney  and 
let  the  paper  cover  the  top  of 

the  Chimney  loosely.      Then  Set      FlG.  ?I.   Testing  the  air  in  the  lamp 

the   chimney   over   a   burning          chimney  for  carbon  dioxid. 


no 


Science  for  Beginners 


candle.  The  candle  will  presently  go  out,  after  which  the 
wire  may  be  withdrawn.  Notice  the  cloudy  appearance  of 
the  film  of  water  on  the  wire.  What  was  produced  by  the 
burning  candle  ? 

Exercise  n.  Flush  out  the  chimney  by  washing  it  in 
pure  air.  Clean  the  wire  and  dip  it  again  into  the  limewater. 

Now  hang  it  in  the  clean  chimney 
without  the  candle  and  allow  it 
to  hang  for  as  long  a  time  as  when 
the  candle  was  used.  Does  the 
limewater  become  cloudy  now? 

Where  does  the  carbon  dioxid 
that  was  detected  in  Exercise  10 
come  from?  Why  did  the  can- 
dle go  out?  W7hat  becomes  of 
the  carbon  dioxid  that  is  con- 
stantly being  given  off  into  the 
air?  Perhaps  you  will  not  be 
able  to  answer  this  last  question 
until  you  have  studied  a  later  chapter  in  this  book. 

The  origin  of  coal.  Let  the  pupils  obtain  samples  of 
"  soft,"  or  bituminous,  coal,  and  of  "  hard,"  or  anthracite, 
coal.  What  is  coal  and  where  did  it  come  from  ?  Some- 
times the  prints  of  leaves  can  be  found  in  coal,  and  in 
coal  beds  stumps  and  entire  trunks  of  trees  that  have 
been  turned  into  coal  have  been  found.  Because  of 
facts  like  these  scientists  believe  that  our  coal  has  been 
formed  from  great  masses  of  vegetation  that  millions 
of  years  ago  collected  in  swamps  and  became  buried 
in  the  earth.  Under  the  influence  of  heat,  moisture, 
and  pressure  a  process  of  slow  distillation,*  much  like 


FIG.  72.     Prints  of  fern  leaves 
in  coal. 


Carbon  and  Its  Compounds 


in 


FIG.  73.     A  forest  of  the  coal  period. 

that  produced  by  heating  wood  in  an  ignition  tube,  was 
carried  on.  In  this  way  much  of  the  material  in  the 
plants  was  driven  off,  leaving  carbon  as  the  chief  ele- 
ment in  the  coal.  Where  the  coal  was  subjected  to 
great  heat,  anthracite  coal  was  produced. 

A  review  of  what  you  have  learned  of  carbon.  Sit 
before  a  coal  fire  and  review  what  you  have  learned 
of  carbon.  Consider  where  this  element  is  found,  its 
different  forms  and  compounds,  its  usefulness  to  man, 
and  other  facts  about  it  that  you  have  learned.  The 
carbon  atoms  of  the  coal,  which  have  for  millions  of 
years  been  imprisoned  in  the  earth,  are  going  forth  to  a 
new  life  in  the  air.  Allow  your  imagination  to  dwell 
upon  their  history  and  upon  what  the  future  holds  in 
store  for  them. 


CHAPTER   THIRTEEN 

A  CAKE  OF  SOAP 

You  are  asked  to  make  a  study  of  this  subject  for 
two  purposes,  —  first  to  learn  some  interesting  facts 
about  an  article  of  everyday  use,  and  secondly  to  find 
in  certain  common  experiences  of  daily  life  some  further 
illustrations  of  the  principles  and  methods  of  chemistry. 

Some  one  has  said  that  the  state  of  civilization  at 
which  a  nation  has  arrived  may  be  measured  by  the 
amount  of  soap  consumed.  In  England  there  are  manu- 
factured over  50  pounds  per  year  for  each  man,  woman, 
and  child.  In  America  the  rate  is  very  nearly  as  high. 
Before  any  conclusion  is  reached  by  putting  these  state- 
ments together,  it  should  be  noted  that  England  sends  a 
large  amount  of  her  soap  to  America,  and  that  Germany, 
France,  and  Holland  do  the  same. 

History  of  soap  and  soap  making.  We  do  not  know 
when  soap  was  first  used,  but  it  must  have  been  at  a  very 
early  day.  Consult  Jeremiah  ii,  22,  and  Malachi  iii,  2. 

In  the  collections  at  the  Louvre,  the  old  royal  palace 
in  Paris,  is  a  vase  supposed  to  be  at  least  2500  years 
old.  It  bears  upon  its  sides  a  picture  of  a  group  of 
children  blowing  soap  bubbles  from  a  pipe. 

Pliny,  the  Roman  historian,  wrote :  "  Prodest  et  sapo ; 
Galliarum  hoc  inventum  rutilandis  capillis.  Fit  ex 
sebo  et  cinere.  Optimus  fagino  et  caprino ;  duobus 
modis,  spissus  ac  liquidus;  uterque  apud  Germanos 
majore  in  usu  viris  quam  feminis."  * 

1"Soap  is  in  common  use;  it  was  discovered  by  the  Gauls  while 
dyeing  their  hair.  It  is  made  of  tallow  and  ashes.  The  best  is  made  of 
beech  ashes  and  the  fat  of  the  goat.  There  are  two  kinds,  the  thick 

112 


A  Cake  of  Soap 


FIG.  74- 


The  above  is  probably 
the  earliest  known  record 
of  the  process  of  soap  mak- 
ing, and  it  is  interesting  to 
note  that  the  method  has 
not  changed  to  any  great 
extent  from  that  day  to 
this.  Pliny,  the  elder, 
perished  at  the  time  of  the 
destruction  of  Pompeii,* 
and  in  the  excavations 
made  at  that  place  has  .been 
found  a  complete  soap- 
making  establishment,  to- 
gether with  some  soap  in  a  perfect  state  of  preservation. 
In  essential  features,  the  method  of  soap  making  used  at 
the  present  time  does  not  differ  from  that  used  by  the 
Pompeians. 

Soap  making  at  an  early  day  in  America.  Forty 
years  ago  the  old-fashioned  process  of  soap  making  was 
a  familiar  sight,  especially  at  the  farmer's  home.  At 
some  place  near  the  kitchen  door  stood  a  barrel  into 
which  were  thrown  all  forms  of  fat.  This  constituted  the 
"  soap  grease,"  which  was  allowed  to  accumulate  until 
spring  came  and  the  soap  was  made.  Then  some  day, 
when  it  was  convenient,  the  "  leach  tub"  was  arranged. 
This  was  a  barrel  placed  upon  blocks  or  upon  a  platform 
tilted  at  a  slight  angle.  Through  the  bottom  of  the 

and  the  liquid.    Among  the  Germans  each  kind  is  in  more  common  use 
among  men  than  among  women." 


H4  Science  for  Beginners 

barrel  several  holes  were  bored.  In  the  bottom  was 
first  placed  some  straw  to  make  room  for  the  lye  to  flow 
out,  then  a  layer  of  lime,  and  then  wood  ashes  to  fill  the 
remainder  of  the  barrel.  The  ashes  were  then  covered 
with  water,  preferably  soft  warm  water.  In  passing 
through  the  ashes  the  water  dissolved  certain  portions  of 
them,  and  when  the  solution  came  into  contact  with  the 
lime  it  changed  chemically  into  what  was  known  as  "  lye." 

Exercise  i.  Make  a  small  leach  tub  in  any  way  convenient. 
A  small  box  or,  better,  a  large  glass  funnel  and  filter  paper 
may  be  used.  Use  no  lime.  You  may  accomplish  the  same 
result  by  adding  hot  water  to  wood  ashes  in  a  dish  and  in 
this  way  dissolving  from  the  ashes  whatever  is  soluble.  Test 
this  solution  with  red  litmus  paper. 

Now  "  boil  down  "  the  lye ;  the  chemist  would  say  "  con- 
centrate it,"  or  "  evaporate  nearly  to  dryness."  When  this 
has  been  done,  apply  a  few  drops  of  acid  and  notice  the 
very  sudden  effervescence.*  Pass  the  gas  thus  produced 
into  lime  water  by  the  method  described  on  page  109  and 
convince  yourself  that  it  is  carbon  dioxid. 

You  have  now  discovered  two  things  concerning  the 
lye :  (i)  it  is  strongly  alkaline,  as  shown  by  the  litmus 
paper;  and  (2)  it  contains  carbon  dioxid,  from  which 
fact  we  may  conclude  that  the  ashes  contain  a  carbonate. 
Putting  the  two  facts  together,  we  may  conclude  that 
the  ashes  contain  an  alkaline  carbonate.  This  may  not 
mean  much  to  the  beginner  in  chemistry,  but  the  trained 
chemist  will  know  at  once,  from  the  above  evidence, 
that  the  ashes  contain  either  potassium  or  sodium 
carbonate.  Which  of  these  two  it  is  he  may  determine 
by  experiment. 


A  Cake  of  Soap  115 

Exercise  2.  Make  the  flame  test  for  potassium  as  directed 
in  Exercise  8,  page  77. 

The  flame  test  may  often  be  used  for  the  detection 
of  other  metals.  If  the  laboratory  of  the  school  can 
furnish  small  amounts  of  the  salts  of  the  metals  that 
are  mentioned  in  the  next  exercise,  these  tests  may  well 
be  learned  by  actual  experiment. 

The  general  method  of  making  these  tests  is  as  follows : 
A  wire  is  dipped  into  the  powdered  solid  or  concen- 
trated solution  of  the  substance  to  be  tested,  and  held 
in  the  flame.  Each  metal  will  give  a  different  color  to 
the  flame.  The  wire  must  be  thoroughly  cleaned 
before  and  after  every  test  by  dipping  it  in  the  acid 
and  holding  it  in  the  flame  until  all  foreign  matter  is 
removed  from  the  wire. 

The  metal  sodium  gives  an  instant  flash  of  bright 
yellow.  This  color  is  absorbed*  when  a  blue  (cobalt) 
glass  is  held  between  the  flame  and  the  eye  of  the  ob- 
server. The  glass  should  be  held  at  arm's  length  from 
the  eye  and  not  too  close  to  the  flame. 

The  metal  potassium  gives  from  its  compounds 
violet  or  reddish  violet  color.  This  is  not  absorbed* 
by  the  blue  glass.  It  is  made  invisible  by  sodium  if 
that  metal  is  present. 

Exercise  3.  (i)  Test  a  pure  solution  of  common  salt  with 
and  without  the  blue  glass. 

(2)  Repeat    the   experiment,    using   some   compound   of 
potassium,  preferably  the  chlorid. 

(3)  Now  test  a  mixture  of  salts  of  the  two  metals,  with 
and  without  the  blue  glass.     Can  you  see  with  the  unaided 


n6  Science  for  Beginners 

eye  the  lilac  color  produced  by  the  potassium?    Can  you 
see  it  when  the  blue  glass  is  used? 

Compounds  of  strontium  color  the  flame  crimson. 
Such  compounds  are  much  used  in  fireworks. 

A  red  color  may  be  obtained  from  compounds  of  cal- 
cium or  of  lithium.  Make  the  tests  and  compare  the 
flames.  Which  is  the  brighter? 

Compounds  of  zinc  impart  a  bluish  white  color  to  the 
flame. 

A  green  color  may  be  given  by  hydrochloric  acid, 
compounds  of  boron,  salts  of  barium,  or  copper  (except 
the  chlorid). 

A  blue  color  indicates  copper  chlorid,  or  compounds  of 
lead,  arsenic,  or  antimony. 

Potassium  in  solution  from  ashes.  A  delicate  lilac 
color  will  be  produced  from  the  solution  of  the  ashes, 
and  we  therefore  conclude  that  wood  ashes  contain  a 
compound  known  as  potassium  carbonate,  or  carbonate  of 
potash.  Its  chemical  formula  is  K2CO3. 

The  old-fashioned  leach  tub,  however,  contained  lime 
in  the  bottom,  and  we  must  now  inquire  about  the  effect 
which  this  produced  upon  the  potassium  carbonate  dis- 
solved out  of  the  ashes. 

Exercise  4.  Add  a  considerable  quantity  of  quicklime 
to  the  solution  obtained  from  the  ashes.  Stir  it  thoroughly 
and,  when  it  is  settled,  pour  off  the  clear  liquid.  This  is  lye. 
Save  the  solid  for  future  testing. 

Concentrate  the  lye  by  boiling,  and  test  with  the  acid, 
the  wire,  and  the  litmus  paper.  It  is  strongly  alkaline ;  it 
gives  the  flame  test  for  potassium ;  but  it  does  not  effervesce 


A  Cake  of  Soap  117 

with  the  acid  and  therefore  is  not  a  carbonate,  —  that  is, 
it  does  not  contain  carbon  dioxid. 

Exercise  5.  Test  with  acid  some  of  the  lime  that  was  used 
in  making  the  lye.  It  effervesces  with  the  acid  and  therefore 
contains  carbon  dioxid. 

It  appears,  then,  that  there  has  been  a  chemical  action 
between  the  lime  and  the  substance  obtained  from  the 
ashes ;  the  carbon  dioxid  has  left  the  potassium  and 
united  with  the  lime.  By  this  process  lye  and  carbonate 
of  lime  have  been  produced.  What  has  happened  may 
be  told  in  the  following  way: 

Potassium  carbonate  +  lime  — >  lye  -f-  carbonate  of  lime 

Putting  together  the  results  we  have  obtained  in 
Exercises  3  and  4,  we  may  write  the  following  story  of 
all  that  happened  in  the  leach  tub : 

Wood  ashes  +  water  +  lime  — >•  lye  +  carbonate  of  lime 

When  the  lime  is  used  in  the  leach  tub,  the  carbonate 
of  lime,  being  insoluble  in  the  water,  remains  in  the 
leach  tub,  while  the  lye,  which  is  soluble  in  water,  runs 
through.  Lye  from  wood  ashes  is  known  chemically  as 
potassium  hydroxid  (KOH),  or  potash.  It  is  manu- 
factured in  large  quantities  for  commercial  and  chemical 
purposes  and  is  found  in  every  chemical  laboratory. 

Making  the  soap.  Following  the  making  of  the  lye 
comes  the  day  when  the  soap  is  to  be  made.  A  large 
iron  kettle  is  procured ;  the  fat  is  put  into  it  with  the  lye 
in  about  the  proportion  of  100  pounds  of  fat  to  25  pounds 
of  weak  lye,  and  the  two  are  boiled  together.  After 
several  hours  the  fat  and  the  lye  have  acted  upon  each 


n8 


Science  for  Beginners 


other  chemically  and  soft 
soap  is  produced.  If  this  is 
taken  into  the  hand,  it 
may  "  take  hold  "  strongly, 
not  only  cleansing  the  hand 
of  dirt,  but  also  acting  upon 
the  skin  itself.  In  this  case, 
there  has  been  too  much  lye 
and  not  enough  fat.  If,  on 
the  contrary,  the  product 
feels  slippery  and  greasy,  it 
is  likely  that  there  was  not 
lye  enough.  It  is  difficult 
to  adapt*  the  fat  and  lye 
to  each  other  in  exactly 
the  right  proportions  by 
merely  guessing.  So,  in  fac- 
tories where  soap  is  made 
in  great  vats,  the  chemist  is 
asked  to  determine  exactly 
how  much  lye  and  fat  shall  be  used. 

Glycerin.  When  properly  made,  soft  soap  is  very 
pleasant  to  the  sense  of  touch.  This  is  because  it  con- 
tains glycerin.  The  exact  story  of  soap  making  may  be 
told  as  follows : 

Fat  -f-  lye  ->  soap  +  glycerin 

The  soap  and  the  glycerin  are  mixed  together ;  and  it 
is  impossible  to  separate  the  glycerin  from  soft  soap. 
But  when  hard  soap  is  manufactured  the  separation  can 
be  made. 


Lark  in  Soap  Company 
FIG.  75.  A  great  vat  in  a  soap  factory. 
It  extends  from  the  basement  through 
3  floors  of  the  factory ;  holds  750  tons ; 
and  has  in  it  i^  miles  of  steam  pipe 
for  heating  the  soap  materials. 


A  Cake  of  Soap  119 

Hard  soap.  The  difference  between  soft  soap  and 
hard  soap  is  due  to  the  materials  contained  in  them. 
The  lye  in  wood  ashes  contains  potassium,  and  potas- 
sium soaps  are  soft.  To  make  a  hard  soap  a  soda  lye 
(caustic  soda,  or  NaOH)  is  used.  This  is  purchased  by 
the  farmer's  wife  as  "  concentrated  lye,"  and  the  chemist 
keeps  it  in  a  purified  form  on  his  shelf. 

In  making  hard  soap  the  soda  lye  and  fat  are  first 
boiled  together,  and  when  the  contents  of  the  kettle 
have  become  thoroughly  united,  a  strong  solution  of 
common  salt  is  added  and  the  mixture  is  heated  again. 
Then  the  boiling  is  stopped  and  the  kettle  is  left  standing 
for  several  hours.  The  contents  of  the  kettle  separate 
into  two  portions,  the  upper  consisting  of  soap  and  the 
lower  containing  the  excess  of  salt,  glycerin,  and  all  im- 
purities. The  soap  thus  produced  is  hard  soap. 

The  glycerin  is  separated  from  the  water  and  is  used 
in  medicine.  When  glycerin  is  treated  with  nitric 
acid  it  becomes  nitroglycerin,  used  in  making  dynamite* 
and  other  explosives. 

Free  alkali  in  soap.  In  the  making  of  soaps  on  a 
large  scale,  great  care  is  taken  to  use  the  lye  and  the 
fat  in  exactly  the  right  proportions,  to  avoid  an  excess 
of  either  fat  or  lye.  If  too  much  lye  is  used,  a  part  of  it 
remains  in  the  soap  as  a  free  alkali,  which  is  very  irritat- 
ing to  sensitive  skins.  Ordinary  soap  is  not  suitable  for 
toilet  purposes  because  usually  it  contains  an  excess  of 
lye.  The  presence  of  free  alkali  in  a  soap  may  .be  de- 
tected by  dissolving  some  of  the  soap  in  water  and 
testing  it  with  red  litmus  paper. 


I2O  Science  for  Beginners 

Toilet  soaps.  In  preparing  some  of  the  high-grade 
toilet  soaps  the  raw  materials  used  are  of  a  finer  quality. 
For  example,  in  the  making  of  Castile  soap  olive  oil  is 
used  instead  of  animal  fat,  and  in  the  manufacture  of 
many  soaps  perfumes  and  coloring  matters  are  mixed 
with  the  other  materials.  The  mixture  is  then  molded 
into  bars,  cut  into  proper  lengths,  and  stamped  into 
cakes.  A  high  polish  is  given  the  cakes  by  rubbing  them 
with  a  cloth  dipped  in  alcohol.  By  beating  bubbles  of 
air  into  soap  while  it  is  still  in  liquid  form  it  is  made 
light  enough  to  float  on  the  water.  Glycerin  soaps  are 
made  by  melting  hard  soap  and  adding  an  equal  amount 
of  glycerin. 

What  happens  when  we  wash  our  hands.  Soap  is 
used  in  removing  grease  or  dirt  from  either  clothes  or 
the  skin.  We  shall  try  to  understand  what  happens 
when  we  wash  our  hands  with  soap. 

Exercise  6.  With  any  toilet  soap  make  a  lather  on  your 
hands.  Then  hold  the  hands  under  a  faucet  or  wash  them 
in  a  vessel  of  water.  Notice  how  the  lather  slips  off  the 
hands,  carrying  the  dirt  and  grease  with  it. 

Exercise  7.  Put  some  kerosene  or  other  form  of  oil  into 
a  test  tube  partly  filled  with  water.  Shake  the  mixture 
vigorously  and  notice  that  the  oil  or  fat  has  been  broken 
up  into  small  droplets.  Let  it  stand  a  short  time ;  you  will 
notice  that  the  oil  has  run  together  and  that  it  has  risen  to 
the  top  of  the  water. 

Exercise  8.  Repeat  Exercise  7,  but  use  the  white  of  an 
egg  in  place  of  the  water.  Notice  that  the  oil  is  broken  as 
before  into  droplets  and  that  the  droplets  remain  in  that 
condition,  each  one  being  surrounded  by,  or  incased  in, 


A  Cake  of  Soap 


121 


FIG.  76.  Water  and  oil  will  not  mix,  but  if 
white  of  egg  be  shaken  with  oil,  the  oil  is 
broken  into  small  droplets  that  remain 
separate. 


a  portion  of  the  albu- 
men* of  the  egg.  This 
forms  what  is  called  an 
emulsion.  The  oil  or  fat 
is  said  to  be  emulsified. 

Exercise  8.  Repeat 
Exercise  9,  but  use  a 
dilute  solution  of  soap 
with  the  oil.  Shake  it 
thoroughly  and  let  it 
stand.  Does  the  action 
of  the  soap  solution  re- 
semble the  action  of  the 
water  or  the  action  of 
the  white  of  the  egg? 

Study  the  matter  until  you  are  convinced   that   the  soap 
forms  a  true  emulsion  with  the  fat. 

Do  you  now  understand  that  soap  removes  grease  or 
oil  from  your  hands  by  breaking  it  up  into  tiny  droplets 
that  are  washed  away  by  the  water  ?  If  you  wished  to 
wash  your  hands  in  the  most  efficient  and  economical 
manner,  would  you  put  the  cake  of  soap  into  the  basin 
of  water  or  wet  the  hands  and  rub  the  soap  on  them  ? 
Think  over  this  question  until  you  reach  a  conclusion. 
Then  verify  your  conclusion  by  the  method  of  experi- 
ment. 

Hard  waters.  Waters  that  have  drained  through  the 
earth  often  have  dissolved  in  them  certain  chemical 
salts,  especially  calcium  carbonate,  which  make  them 
"hard."  The  "soap  test"  is  a  simple  method  of  de- 
termining whether  a  water  is  hard  or  soft. 


122  Science  for  Beginners 

Exercise  10.  Take  a  basin  of  rain  water  and  a  basin  of 
well  water.  With  a  small  amount  of  toilet  soap,  wash  the 
hands  in  each  basin.  Notice  (i)  that  the  rain  water  forms 
a  lather  at  once,  (2)  that  a  white  precipitate*  resembling 
curds  appears  in  the  well  water,  and  (3)  that  it  takes  longer 
to  make  a  lather  in  the  well  water  than  in  the  rain  water. 
Notice  the  feel  of  the  precipitate  in  the  well  water.  Why 
is  water  of  this  kind  called  hard  ? 

When  soap  is  used  with  hard  water  it  first  forms  a 
chemical  compound  with  the  salts  in  the  water.  This 
compound  is  "  thrown  down,"  or  precipitated,  in  the 
form  of  the  white  substance  which  we  see  and  feel  in 
the  water.  By  this  first  process  the  "hardness  "  of  the 
water  is  removed,  and  it  is  only  after  this  has  been  done 
and  the  water  has  been  made  soft  that  the  cleansing 
process  proper  can  begin. 

Material  used  in  the  manufacture  of  soaps.  Soaps 
are  often  adulterated*  by  the  addition  of  some  cheap 
bulky  materials,  for  the  purpose  of  giving  them  a  false 
weight  or  appearance.  Rosin*  is  added  to  laundry 
soap  to  give  it  a  yellow  color  and  also  to  make  it  lather 
freely.  For  the  same  reason  shaving  soap  contains 
rosin  and  some  proportion  of  potassium  soap  to  make 
it  soft.  Some  soaps  contain  a  high  percentage  of 
water.  Some  toilet  soaps  contain  an  ingredient  which 
is  supposed  to  have  a  medicinal  value.  Scouring 
soaps  are  made  by  adding  finely  ground  sand  or  pumice 
stone.  Great  quantities  of  coconut  oil  are  used  in  soap 
making,  and  much  cottonseed  oil  is  used  for  the  same 
purpose. 


A  Cake  of  Soap  123 

A  concluding  exercise.  As  a  conclusion  to  this 
chapter,  you  may  make  for  yourself  a  sample  of  soap 
to  be  kept  as  a  souvenir  of  your  study  of  one  of  the 
common  articles  of  everyday  life. 

Exercise  u.  Melt  i-J-  ounces  of  olive  or  cottonseed  oil  with 
i  ounce  of  good  tallow  in  a  large  evaporating  dish  or  tin 
basin.  Then  add  a  solution  of  not  more  than  an  ounce  of 
sodium  hydroxid  (NaOH)  dissolved  in  2  ounces  of  water. 

Heat  the  substance  gradually  until  chemical  action,  or 
what  is  known  as  saponification,  takes  place.  Remove 
the  heat  if  the  contents  of  the  dish  tend  to  boil  over.  When 
the  action  ceases,  apply  heat  again  and  boil  gently  for  15 
minutes.  Now  add  -£  ounce  of  common  salt,  and  boil  for 
•J  hour.  The  hard  soap  will  rise  to  the  top  and  may  be 
removed.  Place  the  soap  in  a  shallow  tin  or  pasteboard 
box  to  mold  and  allow  it  to  cool.  Test  the  soap  for  its 
power  to  form  a  good  lather. 


CHAPTER  FOURTEEN 

A  LOAF  OF  BREAD 

BREAD  is  the  sign  of  plenty  and  the  symbol  of  comfort. 
The  cry  of  a  starving  person  or  nation  is  for  bread ;  the 

description  of  hard  times  in 
a  large  city  will  always  in- 
clude the  bread  line.  Bread 
is  the  most  important  of 
all  the  foods  that  must  be 
provided  for  an  army,  and 

in  war  time  the  bake  oven  follows  the  army  as  faithfully 
and  persistently  as  the  soldier  follows  the  flag.  Very 
properly  has  bread  been  called  the  "  staff  of  life."  All  races 
of  men,  even  the  most  barbarous,  have  learned  how  to  grind 
various  kinds  of  cereals*  — wheat,  corn,  barley,  and  rye  — 
into  flour  or  meal  for  making  this  staple  article  of  food. 
The  value  of  bread  as  a  food  is  shown  by  the  way  one 
explorer  subsisted  for  weeks  chiefly  upon  the  various 
kinds  of  bread  which  his  Indian  guide  made  from  flour. 
When  the  Indian  merely  mixed  the  flour  with  water, 
added  a  little  salt  and  boiled  the  dough  in  water,  he 
had  what  he  called  a  "  slippery-go-do wn ";  when  he 
boiled  the  dough  in  the  fat  extracted  from  the  animals 
he  had  captured,  he  had  what  he  called  a  "  dough-god  " ; 
and  he  made  a  "  bannock  "  by  synply  mixing  the 'flour 
into  a  stiff  dough,  allowing  it  to  sour,  adding  a  little 
soda  when  he  had  it,  putting  it  into  the  spider  or  skillet 
in  which  he  had  fried  his  bacon,  and  setting  it  before  his 
camp  fire  to  bake.  He  turned  the  bannock  over  once 
or  twice  in  order  to  form  a  thick  crust  on  both  sides, 

124 


A  Loaf  of  Bread 


125 


Ward  Baking  Company 

FIG.  78.  Bread  mixers  in  a  bakery.  Each  mixer  holds  dough  for  1600  loaves 
of  bread  and  is  operated  by  an  electric  motor.  Note  how  the  wheels  are  pro- 
tected to  keep  the  workmen  from  being  caught  in  them. 

and  when  the  baking  was  done  the  traveler  and  his 
guide  and  cook  would  split  the  bannock  into  two  parts, 
insert  a  few  strips  of  freshly  cooked  bacon  between  them, 
and  thus  have  a  dish  "  fit  for  a  king." 

How  bread  making  should  be  studied.  In  every  manu- 
facturing business  today  the  greatest  care  is  taken  to 
give  attention  to  three  phases  of  the  work.  In  the  first 
place,  there  are  the  materials  that  enter  into  the  manu- 
facture. These  are  called  the  raw  materials,  and  they 
must  be  thoroughly  examined  to  see  that  they  possess 
the  qualities  to  fulfill  exactly  the  purposes  for  which  they 
are  to  be  used.  In  the  second  place,  there  must  be  a 
clear  idea  of  the  finished  product,  of  what  it  is  that  is  to 
be  made.  In  the  third  place,  there  must  be  both  a  clear 


126  Science  for  Beginners 

understanding  of  the  steps  of  the  process  by  which  the 
raw  materials  are  converted  into  the  finished  product, 
and  a  skilled  worker  who  can  carry  the  process  to  suc- 
cessful completion.  We  shall  study  the  three  phases  of 
the  process  of  bread  making,  but  during  our  study  we 
shall  not  attempt  to  keep  the  phases  of  the  subject 
separate  and  distinct. 

What  bread  is.  Bread  is  a  product  manufactured  by 
the  process  of  baking  a  mixture  of  flour  and  water  or 
milk.  Salt  and  yeast  are  also  generally  used  in  the 
making  of  bread,  and  potatoes  are  often  added.  If  we 
use  the  term  "  bread  "  in  its  widest  sense,  we  must  also 
include  among  our  raw  materials  butter  and  other  fats, 
eggs,  raisins,  baking  soda,  and  baking  powder. 

A  cookbook  formula  for  four  loaves  of  potato  bread. 
"  Two  quarts  of  warm  water,  six  boiled  and  mashed 
potatoes,  one  tablespoon  of  sugar,  one-half  tablespoon 
of  salt,  a  piece  of  compressed  yeast  the  size  of  a  pea, 
and  flour  enough  to  produce  a  thick  batter.  Beat  well 
together,  cover,  and  set  in  a  warm  place  to  rise.  When 
light,  mix  thoroughly  with  sufficient  flour  for  a  dough 
as  soft  as  can  be  handled.  When  again  risen,  mold 
lightly,  put  into  tins,  and  set  in  a  warm  place  to  rise. 
When  light,  bake  one-half  hour.  If  the  sponge*  is  set  at 
tea  time,  it  will  be  ready  to  mix  by  bedtime,  and  the 
bread  will  be  ready  for  the  loaves  in  the  early  morning." 
This  is  one  way  of  telling  the  story  of  how  to  make 
bread,  and  the  following  paragraph*  is  another. 

Aunt  Katharine's  cookies.  "  Wai,  I  takes  a  yaller 
bowl,  an'  de  yaller  bowl  mustn't  have  no  spout.  In 


A  Loaf  of  Bread  127 

dat  yaller  bowl,  I  dumps  a  hunk  o'  butter,  den  I  th'ows 
in  a  good  mess  o'  sugar  so  dey'll  be  nice  an'  crisp,  an'  I 
mixes  'em  good.  Den  comes  de  aigs,  —  ef  dey's  cheap, 
I  takes  fo' ;  ef  I  feels  a  little  close,  I  takes  three ;  ef  dey's 
dear,  I  takes  two  ;  one'll  do  well,  an'  ef  dey's  very  dear, 
I  leaves  out  de  aigs  an'  don't  use  no  aigs  at  all.  Den 
I  mixes  in  de  aigs  or  no  aigs,  dumps  in  flour,  bakin'  pow- 
der, milk,  an'  seasonin'.  For  seasoning  I  uses  my  jedg- 
ment  —  sometimes  it's  one  thing,  sometimes  another. 
Den  I  mixes,  rolls,  cuts,  bakes,  an'  eats." 

Scientific  bread  making.  Neither  of  these  receipts  is 
complete  enough  for  the  scientific  bread  maker.  For 
example,  both  tell  us  to  use  flour,  but  what  is  flour  ?  Is 
it  a  pure  substance  or  a  mixture  of  several  different  sub- 
stances ?  What  is  good  flour  and  how  shall  we  be  able  to 
distinguish  good  flour  from  bad  ?  What  is  yeast,  and  what 
part  does  it  play  in  bread  making  ?  At  what  temperature 
will  the  yeast  do  its  best  work?  How  hot  should  the 
oven  be  in  order  that  the  baking  may  be  done  properly  ? 
What  is  the  effect  of  adding  the  potatoes?  These  and 
many  other  questions  must  be  asked  and  answered  before 
one  can  claim  to  have  a  scientific  knowledge  of  the  process 
of  bread  making. 

What  flour  is.  An  experiment  will  bring  to  light  a 
partial  answer  to  the  question,  What  is  flour  ? 

Exercise  i.  Take,  a  small  linen  handkerchief  or  square  of 
muslin  or  cheesecloth,  place  upon  it  some  flour,  bring  the  corners 
of  the  cloth  together,  and  tie  them  with  a  string.  Hold  this 
bag  in  a  dish  of  pure  water  and  knead  it  thoroughly  with  the 
hand.  The  water  becomes  white  with  starch  from  the  flour. 


128  Science  for  Beginners 

Pour  the  water  into  a  tall,  narrow  vessel  and  set  it  aside. 
Continue  to  wash  the  material  in  the  bag  until  the  water 
ceases  to  be  made  milky ;  in  this  way  remove  all  the  starch. 

By  this  process  the  flour  has  been  separated  into  the 
starch,  which  has  been  washed  out  by  the  water,  and  the 
gluten,  which  remains  in  the  bag.  Both  gluten  and 
starch  are  valuable  foodstuffs.  Each  of  these  must  now 
be  examined. 

Exercise  2.  Examine  the  residue  left  from  the  washing 
of  the  flour.  This  is  gluten.  Note  its  color.  The  gluten 
from  good  flour  is  somewhat  yellow ;  that  from  old  and  poor 
flour  is  grayish.  Good  flour  yields  a  gluten  that  is  tough  and 
elastic;  when  pressed  in  the  hand  it  springs  back  into  its 
original  shape  and  it  is  not  easily  broken  into  parts.  The 
gluten  of  poor  flour  lacks  these  qualities. 

An  experienced  miller  will  take  some  flour  in  his  hand, 
wash  it  out  in  water,  and  determine  whether  it  possesses 
the  qualities  which  have  just  been  mentioned.  Some- 
times he  will  weigh  the  flour  before  washing  it  and  then 
dry  and  weigh  the  gluten  he  obtains.  He  then  knows 
the  per  cent  of  gluten  which  the  flour  yields.  How  does 
he  compute  the  percentage?  A  good  wheat  flour  may 
contain  from  10  to  12  per  cent  of  gluten. 

Gluten  a  protein.  Gluten  is  a  protein,  the  class  of  foods 
from  which  the  living  material  of  the  body  is  built. 
Chemically  considered,  it  contains  nitrogen,  an  element 
that  enters  into  the  composition  of  all  living  tissues. 

Exercise  3.  Take  a  small  amount  of  water  in  a  test  tube. 
Add  a  little  of  the  gluten  and  a  few  drops  of  nitric  acid  (HNOa), 
and  boil.  A  yellow  color  appears. 


A  Loaf  of  Bread  129 

Add  a  few  drops  of  ammonium  hydroxid  [NH4(OH)]  and 
re-heat.  The  orange  color  shows  that  a  protein  is  present.1 

The  outer  layers  of  the  wheat  grain  are  richer  in 
gluten  than  the  heart  of  the  grain.  It  therefore  follows 
that  whole  wheat  flour  is  richer  in  gluten  than  fine  white 
flour,  which  is  made  largely  from  the  middle  of  the  kernels. 
However,  dough  made  from  white  flour  rises  more  easily 
than  dough  made  from  whole  wheat  floor,  and  white  bread 
is  usually  lighter  than  brown  bread.  Different  varieties 
of  wheat  differ  in  the  amount  of  gluten  they  contain. 

Exercise  4.  Test  different  foodstuffs  for  protein,  —  bread, 
meat,  potatoes,  oatmeal,  etc.  Make  a  table  showing  together 
the  results  of  this  exercise  and  of  Exercise  6. 

Gluten  important  in  causing  bread  to  rise.  Without 
gluten  in  the  flour  it  would  be  impossible  to  make  bread 
rise.  When  mixed  with  water  the  gluten  becomes  viscid,* 
or  sticky,  and  in  this  condition  prevents  the  escape  of 
gases  that  may  be  in  the  dough.  During  the  baking, 
part  of  the  water  of  the  bread  is  converted  into  steam ; 
there  are  also  carbon  dioxid  from  the  yeast  or  baking 
powder  and  bubbles  of  air  in  the  dough.  The  heating 
causes  all  these  gases  to  expand,  and  they  form  little 
pockets  in  the  sticky  gluten,  thus  causing  the  bread  to 
rise.  During  the  baking,  the  walls  surrounding  these 
little  cavities  are  hardened,  and  the  openings  made  by 
the  gases  remain  in  the  bread  after  baking,  causing  it 
to  be  light  and  porous.  What  do  you  suppose  happens 

1  Another  method  of  testing  for  protein  is  to  add  sodium  hydroxid 
(NaOH)  or  potassium  hydroxid  (KOH),  and  a  few  drops  of  a  very  weak  solu- 
tion of  copper  sulf  ate  (CuSO4) .  If  protein  is  present,  a  violet  color  appears. 


130 


Science  for  Beginners 


when  a  cake  ' '  falls ' '  ?  By  work- 
ing small  bubbles  of  air  into  the 
dough,  "  beaten  biscuit "  are 
made  to  rise. 

Starch  in  flour.  Starch  forms 
more  than  one  half  of  the  solid 
matter  of  grains,  such  as  wheat, 
rye,  oats,  and  corn,  and  it  is  the 
principal  element  of  flour.  The 
starch  left  in  the  water  when 
the  flour  is  washed  (Exercise  i) 
is  not  dissolved  and  after  a  time 
will  settle  as  a  fine  sediment  hi 
the  bottom  of  the  vessel  contain- 
ing the  water. 

Exercise  5.  Remove  from  the 
vessel  set  aside  in  Exercise  i  the 
water  that  is  above  the  starch.  This  may  be  done  by 
siphoning  off  the  water  with  a  piece  of  rubber  tubing ;  or  the 
water  may  be  removed  with  a  pipette  without  disturbing 
the  starch.  Boil  some  of  the  starch  in  water.  It  seems  to 
dissolve  in  the  hot  water  into  an  almost  clear  liquid,  but 
when  it  stands  and  cools  it  forms  a  jelly  or  paste.  This  is  one 
of  the  characteristic  properties  of  starch. 

Add  a  small  amount  of  tincture  of  iodin  to  some  of  the 
boiled  starch.  The  starch  turns  blue.  This  is  a  peculiar 
characteristic  of  starch,  and  the  presence  of  starch  in  any  sub- 
stance may  be  detected  by  the  use  of  iodin.1  Raw  starch  also 
is  turned  blue  by  iodin,  but  the  action  is  slower. 

1  The  tincture  of  iodin  is  prepared  by  dissolving  a  small  piece  of  iodin 
in  alcohol.  Iodin  will  not  dissolve  in  water,  but  a  solution  may  be  made 


FIG.  70.  A  pipette  of  the  kind 
used  in  chemical  laboratories. 
The  liquid  is  drawn  into  the 
pipette  with  the  mouth. 


A  Loaf  of  Bread 


FIG.  80.     Grains  of  starch  as 
seen  under  the  microscope. 


Exercise  6.  Test  different  foodstuffs  for  starch  and  record 
the  results  in  your  notebook. 

Exercise  7.  Scrape  a  potato,  lay  a  small  amount  of  the 
scrapings  on  a  glass  slide,  add  a  drop  of  water,  place  over  it 
a  cover  glass,  and  examine  it  under 
the  microscope.  The  starch  grains 
may  be  clearly  seen. 

Starch  grains  from  different 
plants  vary  in  size  and  form,  so 
that  the  source  of  starch  can  be 
determined  by  examination  under 
the  microscope. 

Dextrin.  When  starch  is  heated, 
as  in  the  baking  of  bread,  the 
molecules  are  broken  up  into  a  substance  known  as 
dextrin,  which  is  somewhat  sweet  to  the  taste.  Dextrin 
is  found  in  the  crust  of  bread.  It  is  a  gum,  and  great 
quantities  of  it  are  used  in  the  manufacture  of  mucilage. 
It  is  used  on  the  backs  of  postage  stamps  and  in  sealing 
envelopes.  In  the  crust  of  the  bread  some  of  the  dextrin 
is  still  further  changed  to  caramel. 

How  starch  is  used  by  the  body.  First  the  saliva 
changes  the  starch  into  dextrin,  and  then  the  dextrin  is 
still  further  broken  up  into  a  sugar.  The  sugar  is  readily 
soluble  in  water  and  can  be  absorbed  into  the  blood  and 
distributed  to  all  parts  of  the  body.  The  great  use  of 
sugar  in  the  body  is  to  furnish  heat  and  to  give  energy 
to  the  muscles,  while  the  proteins  are  the  foods  that  are 

by  dissolving  potassium  iodid  in  water  and  then  dissolving  the  iodin  in 
this  solution.  Two  parts  of  iodin  and  15  parts  of  potassium  iodid  to  100 
parts  of  water  will  make  a  solution  of  the  right  strength. 


132  Science  for  Beginners 

used  in  building  the  cells  and  tissues  of  the  body.  It  will 
thus  be  seen  that  bread  furnishes  to  the  body  both  build- 
ing material  and  energy. 

Yeast  and  its  action.  The 
yeasts  are  a  group  of  living 
plants,  all  so  small  that  they 
can  be  seen  only  by  the  use 

FIG.  81.    Yeast  plants  as  seen  under       Of  amicroSCOpe.    Each  plant 
the  microscope.  .  . 

consists  of  but  a  single  cell. 

They  feed  upon  sugar  and  starchy  materials  and  also 
require  that  a  part  of  their  food  shall  contain  nitrogen. 
They  grow  and  multiply  very  rapidly.  As  they  grow, 
they  produce  a  certain  substance  which  has  the  curious 
effect  of  changing  sugar  into  alcohol  and  carbon  dioxid. 
The  chemist  would  write  the  story  of  the  change  which 
the  yeast  produces  as  follows : 

C6Hi206  ->  2  C2H5OH  +   2  C02 

sugar       — >  alcohol          +  carbon  dioxid 

In  bread  making  the  carbon  dioxid  given  off  by  the 
yeast  is  the  most  important  factor  in  causing  the  dough 
to  rise.  The  bubbles  of  the  gas  are  caught  by  the  elastic 
gluten  of  the  flour  and  held  long  enough  to  expand  the 
dough  to  double  its  size  or  more.  Before  the  end  of  the 
baking,  the  gas  as  well  as  the  alcohol  vapor  escapes, 
leaving  the  bread  light  and  porous.  When  eggs  are 
added  to  bread  they  assist  in  the  rising  of  the  bread 
by  making  the  dough  or  batter  tough  and  sticky  so 
that  it  will  hold  the  expanding  gases.  Very  commonly, 
too,  air  is  beaten  into  the  eggs  before  they  are  added  to 
cake  or  bread. 


A  Loaf  of  Bread  133 

The  best  temperature  for  the  growth  of  yeast.     The 

dough  must  be  kept  at  a  temperature  that  will  allow 
the  yeast  plant  to  grow,  or  the  baker  will  fail  in  the  rais- 
ing of  his  bread.  These  little  plants  thrive  best  between 
the  temperatures  of  70  and  90  degrees  F.  They  are  com- 
pletely destroyed  when  the  temperature  rises  above 
131  degrees ;  if  the  dough  is  overheated,  the  bread  does 
not  rise  and  is  sour  and  unpalatable.  Without  a  ther- 
mometer, how  could  we  keep  the  sponge*  between  the 
temperatures  of  70  and  90  degrees  F.  ?  In  order  to  culti- 
vate your  judgment  in  this  direction,  try  the  following 
exercise : 

Exercise  8.  Pour  into  a  vessel  a  cupful  of  boiling  water 
and  a  cupful  of  water  at  the  temperature  of  the  laboratory 
or  kitchen.  Take  the  temperature  of  the  mixture.  Find, 
by  trial,  how  much  boiling  water  must  be  added  to  a  quart 
of  water  at  ordinary  temperature  to  bring  the  mixture  to  a 
temperature  between  70  and  90  degrees  F.  Should  boiling 
water  be  poured  directly  into  dough? 

In  baking,  of  course,  the  temperature  goes  much 
above  131  degrees  F.,  and  in  consequence  the  living 
yeast  plants  are  destroyed  and  cease  to  produce  carbon 
dioxid.  The  temperature  of  the  large  commercial  ovens 
rises  to  a  temperature  of  400  or  500  degrees  F.  In  the 
ordinary  oven  the  temperature  is  somewhat  lower  than 
this,  about  380  degrees  F.  As  long  as  moisture  remains 
in  the  bread,  the  temperature  of  the  interior  of  the  loaf 
will  not  be  above  that  of  boiling  water. 

The  use  of  potatoes  in  bread  making.  Potatoes  are 
often  used  in  the  making  of  bread.  Not  only  do  they 


134  Science  for  Beginners 

give  their  own  peculiar  flavor  to  the  bread,  but  they  also 
furnish  materials  which  greatly  stimulate  the  growth  of 
the  yeast  plants.  Because  of  this,  less  yeast  may  be  used 
when  potatoes  are  included  in  the  sponge. 

Exercise  9.  Dissolve  thoroughly  about  ^  of  a  cake  of 
compressed  yeast  in  a  small  amount  of  tepid*  water ;  add  to 
it  a  very  small  amount  of  ammonium  chlorid  and  a  table- 
spoonful  of  molasses,  and  pour  the  mixture  into  a  large- 
sized  test  tube  which  is  provided  with  a  delivery  tube.  Add 
warm  water  enough  to  make  the  test  tube  three  quarters  full. 
Put  the  tube  in  a  warm  place,  —  where  the  temperature  will 
be  between  70  and  90  degrees  F. 

Pass  the  gas  which  comes  from  the  delivery  tube  into  a 
solution  of  limewater.  After  a  time  (perhaps  an  hour  or  two) 
the  limewater  will  be  seen  to  contain  a  milky  sediment  (page 
109).  What  does  this  prove?  By  appropriate  apparatus 
it  is  possible  to  separate  out  the  alcohol  which  is  produced 
at  the  same  time  as  the  carbon  dioxid. 

Exercise  10.  After  a  few  hours  mount  on  a  slide  a  drop 
of  the  liquid  in  which  the  yeast  is  growing  and  examine  it 
with  a  microscope.1  It  will  be  found  to  contain  hundreds  of 
small  yeast  plants.  How  do  they  multiply?  The  yeast 
will  be  more  clearly  seen  if  the  drop  of  liquid  examined  is 
taken  from  the  upper  part  of  the  tube  without  stirring  up 
the  fragments  of  the  yeastcake. 

The  only  reason  for  using  yeast  in  bread  is  to  produce 
carbon  dioxid  to  make  the  bread  rise.  It  is  a  great  ad- 
vantage to  have  bread  light  and  filled  everywhere  with 
small  pores,  for  then  the  digestive  juices  can  gain  easy 

1  Yeast  for  examination  may  be  grown  very  easily  in  a  solution  of  sugar 
in  water. 


A  Loaf  of  Bread  135 

access  to  every  part  of  it  and  thus  act  quickly  and  readily 
on  it. 

Helping  the  growth  of  the  yeast.  Sometimes  yeast- 
cake  has  a  disagreeable  flavor  and  odor,  and  if  a  large 
amount  of  it  is  used  in  starting  the  bread  the  objection- 
able taste  may  be  detected  in  the  loaf  after  it  has  been 
baked.  Scientists  have  been  making  careful  studies 
of  how  the  yeast  in  the  bread  can  be  made  to  multiply 
more  rapidly  so  that  only  a  small  amount  of  yeastcake 
need  be  used,  and  recently  they  have  announced  that  a 
very  little  ammonium  chlorid  in  the  sponge  greatly  helps 
the  growth  of  the  yeast.  It  is  also  very  important  that 
the  dough  be  thoroughly  kneaded,  so  that  the  yeast  may 
be  mixed  into  all  parts  of  it. 

Substitutes  for  yeast.  Partly  because  yeast  is  some- 
times poor  and  does  not  do  its  work  well,  but  more  partic- 
ularly because  it  feeds  upon  and  thus  uses  up  some  of  the 
valuable  food  materials  of  the  sponge,  other  substances 
often  are  used  to  produce  carbon  dioxid  in  bread.  Liebig, 
a  great  chemist,  calculated  that  in  Germany  the  daily 
loss  of  good  food  material  by  the  growth  of  the  yeast 
plant  was  sufficient  to  supply  400,000  persons  with  bread. 
There  are  numerous  baking  powders  which  are  used  as 
substitutes  for  yeast.  Any  substance  that  is  used  for 
the  raising  of  bread  should  yield  a  good  supply  of  carbon 
dioxid  and  should  not  leave  harmful  products  in  the  bread. 
The  chief  objections  to  the  use  of  ordinary  baking 
powders  are  that  they  may  be  adulterated  or  badly  pre- 
pared and  therefore  inefficient,  and  that  disagreeable 
or  unwholesome  products  from  them  may  remain  in  the 


136  Science  for  Beginners 

bread.  In  any  case,  they  lack  the  flavor  and  aroma  which 
good  yeast  imparts,  and  yeast  bread  is  still  the  kind  that 
is  most  commonly  made. 

Baking  soda.  Common  baking  soda,  better  known  as 
carbonate  of  soda  (NaHCOs),  may  be  used  to  produce 
carbon  dioxid.  When  mixed  in  the  dough  and  heated, 
it  yields  the  gas ;  but  in  this  case  there  remains  in  the 
bread  sodium  carbonate,  an  alkaline  substance  which 
renders  the  bread  unwholesome.  The  chemical  reaction  is 

2  NaHCO3  ->    Na«C08    +  H20  +     C02 

sodium  bicarbonate  — >•  sodium  carbonate  +    water     +  carbon  dioxid 

Exercise  n.  To  a  water  solution  of  baking  soda  add  a 
few  drops  of  hydrochloric  acid.  Test  the  gas  that  is  given 
off,  by  passing  it  into  limewater. 

NaHCOs    +       HC1       ->     NaCl      +  H2O  +      CO2 

sodium  bicarbonate  +  hydrochloric  acid  — >•  sodium  chlorid  +  water  +  carbon  dioxid 

This  experiment  illustrates  a  method  which  is  used, 
with  many  variations,  to  raise  bread.  For  example,  a 
light  bread  or  pancakes  may  be  made  by  the  use  of 
baking  soda  or  sour  milk.  If  two  teacups  of  sour  milk 
be  added  to  the  flour  and  one  teaspoonful  of  soda  be  well 
mixed  in  just  before  baking,  a  copious  amount  of  the  gas 
is  produced  and  the  bread  is  light.  In  this  case  there  is 
left  in  the  bread  a  compound,  sodium  lactate,  which  is 
harmless.  The  milk  has  contributed  some  good  ingredi- 
ents to  the  bread.  Care  must  be  taken  not  to  use  too 
much  soda,  or  the  bread  will  be  yellow  and  unwhole- 
some. 

Gingerbread.  This  very  palatable  form  of  bread  is 
made  by  the  use  of  baking  soda  and  molasses,  the  acid  of 


A  Loaf  of  Bread 


which,  acting  upon  the  soda,  produces  the  gas.  In  case 
the  molasses  is  not  sufficiently  acid,  a  little  sour  milk  or 
vinegar  may  be  added  to  it  be- 
fore it  is  mixed  with  the  flour. 
Baking  powders.  Among 
the  best  agents  for  the  rais- 
ing of  bread  without  the  use 
of  yeast  are  combinations  of 
baking  soda  with  substances 
that  are  acid  in  their  nature. 
The  one  most  commonly 
used  and  giving  the  best  re- 
sults is  that  known  as  cream 
of  tartar.  The  soda  and 


FIG.  82.    A  review  of  bread  making. 


the  cream  of  tartar  do  not  act  upon  each  other  as  long 
as  they  are  kept  dry,  but  they  react  quickly  when  dis- 
solved in  water.  For  this  reason,  the  cream  of  tartar 
and  the  soda  should  be  mixed  with  the  flour  before 
any  water  is  added.  The  substance  which  is  left  in 
the  bread  is  known  as  "  Rochelle  salts."  The  equation 
which  tells  the  story  of  what  happens  in  the  dough  is 
as  follows : 


NaHC03  +  KHC4H406 

soda  +     cream  of  tartar 


KNaC4H406  +     C02  +H20 

Rochelle  salts        +  carbon  dioxid  +  water 


Exercise  12.  In  separate  glasses  dissolve  small  amounts 
of  baking  soda  and  cream  of  tartar  in  water.  Pour  one  solu- 
tion into  the  other.  Violent  chemical  action  takes  place  and 
carbon  dioxid  is  given  off. 

In  the  baking  powder  that  we  buy  in  the  stores,  the 
baking  soda  is  mixed  with  the  cream  of  tartar,  along 


138  Science  for  Beginners 

with  flour  or  starch  to  absorb  moisture.  It  must  be 
kept  perfectly  dry  until  it  is  to  be  used.  Why? 

Salt-rising  bread.  In  making  salt-rising  bread,  the 
housewife  mixes  corn  meal  with  hot  water  or  milk,  and 
adds  salt  and  a  little  soda.  After  some  hours  this  mix- 
ture ferments  and  carbon  dioxid  is  given  off.  It  is  then 
added  to  dough  in  place  of  yeast  and  the  dough  is  made 
up  as  for  ordinary  bread. 

It  has  been  discovered  that  it  is  a  certain  kind  of  bac- 
terium, and  not  yeast,  that  grows  in  this  mixture  and 
gives  off  carbon  dioxid.  The  bacteria  get  into  the  mix- 
ture from  the  corn  meal  and  grow  best  when  milk  is 
used  in  making  up  the  batter. 

A  practical  review.  For  a  review  of  this  chapter,  get 
your  mother  to  allow  you  to  go  through  the  interesting 
process  of  bread  making.  Follow  directions  closely  and 
give  a  reason  for  each  step  that  you  take.  Are  you  find- 
ing that  science  is  closely  related  to  the  everyday  work 
of  life? 


CHAPTER   FIFTEEN 

THE   LIMESTONE    STORY 

MAKE  a  field  excursion  for  limestone.  This  excursion 
may  be  taken  after  school  on  a  favorable  afternoon,  on 
Saturday,  or  under  the  direction  of  the  teacher  during 
school  hours.  It  may  be  taken  by  the  whole  class  to- 
gether or  by  individual  members.  Much  enjoyment  as 
well  as  profit  may  be  derived  from  excursions  of  this 
kind.  Having  a  definite  object  emphasizes  and  gives 
point  to  the  recreation. 

Carry  with  you  on  your  excursion  a  knife  (an  old 
one  will  do)  and  a  small  vial  of  hydrochloric  acid,  which 
you  may  obtain  at  any  drug  store.  A  geologist  always 
carries  a  strong  hammer  on  his  field  trips,  and  it  might 
be  well  for  you  to  take  with  you  this  useful  article. 
Read  this  chapter  over  carefully  before  you  start,  or 
carry  your  book  with  you  on  your  collecting  tour. 

Exercise  i.  Look  for  stones  that  (i)  are  white  or  gray  in 
color,  (2)  are  easily  scratched  with  a  knife,  and  (3)  give  off 
bubbles  of  gas  when  touched  with  a  drop  of  acid. 

If  you  succeed  in  finding  a  mineral  that  meets  these  three 
tests  and  is  about  one  third  as  heavy  as  iron,  you  may  con- 
clude that  it  is  limestone.  Take  some  good-sized  pieces  home 
with  you  for  study. 

Crystallized  limestone.  Sometimes,  but  not  always, 
a  piece  of  limestone  will  show  bright  surfaces  that 
glisten  in  the  sun.  This  is  due  to  crystals  in  it.  When 
highly  crystallized,  limestone  is  transparent*  and  breaks 
easily  and  smoothly  in  three  directions  in  surfaces 
which  are  nearly  at  right  angles  to  each  other.  Pure 

139 


140 


Science  for  Beginners 


crystallized  limestone  is 
known  as  Iceland  spar,  be- 
cause very  perfect  crystals  of 
the  mineral  are  formed  from 
the  waters  of  the  geysers*  and 
hot  springs  of  Iceland. 

Iceland  spar  has  the  very 
remarkable  property  of  double 
refraction;  that  is,  it  forms 
two  images  of  an  object  that 
is  looked  at  through  i t .  If  you 
place  a  piece  of  Iceland  spar 
on  a  printed  page,  you  will 
see  two  images  of  every  letter. 
The  composition  of  lime- 
stone. We  are  now  to  learn 
the  chemical  composition  of 

limestone,  to  answer  the  question  :  Of  what  is  it  made  ? 
If  you  were  not  successful  in  finding  any  limestone  on 
your  excursion,  you  can  go  to  a  marble  shop  and  get  some 
fragments  of  marble.  This  is  limestone  that  is  composed 
of  very  fine  crystals.  It  has  been  subjected  to  great  heat 
in  the  earth  and  has  crystallized  in  cooling.  See  that  it 
agrees  with  all  the  tests  for  limestone  as  given  in  Exercise  i . 
Exercise  2.  Take  two  test  tubes;  two  small  vials  or 
bottles  will  answer.  In  one  tube  place  a  small  piece  of 
limestone  and  in  the  other  limewater  to  the  depth  of  one 
inch.  Add  a  few  drops  of  acid  to  the  limestone.  Notice  the 
gas  which  is  given  off.  It  is  heavier  than  air  and  can  be 
poured  like  water  from  one  tube  into  the  other.  Hold  the 


FIG.  83.  A  crystal  of  Iceland  spar 
forms  a  double  image  of  an  object 
that  is  seen  through  it. 


The  Limestone  Story    .  141 

tubes  so  that  the  gas  which  comes  from  the  tube  containing 
the  limestone  will  settle  into  the  one  containing  the  limewater. 
After  the  gas  has  been  running  a  minute  or  two,  put  your 
thumb  over  the  mouth  of  the  tube  containing  the  limewater 
and  shake  it  to  mix  the  limewater  and  the  gas  together. 
A  precipitate  appears  in  the  limewater.  What  does  this 
indicate  (Exercise  7,  page  108)  ?  Was  there  carbon  dioxid  in 
the  acid  that  you  used? 

We  have  learned  that  limestone  gives  off  carbon 
dioxid,  and  we  may  conclude  that  it  is  in  part  composed 
of  carbon  and  oxygen.  We  have  also  learned  why  lime- 
stone effervesces  when  it  is  touched  with  an  acid. 

Exercise  3.  Place  pieces  of  limestone  or  marble  of  the 
size  of  a  hickory  nut  on  the  top  of  a  coal  fire,  in  the  oven 
of  a  stove,  or  on  a  piece  of  wire  gauze  over  a  low  flame 
and  let  them  stand  for  some  time.  Examine  a  piece  which 
has  been  treated  in  this  way.  Notice  that  it  has  become 
soft  and  brittle.  Test  it  with  the  acid.  If  sufficiently 
burned  it  will  not  effervesce.  It  is  no  longer  limestone. 
By  heating,  the  limestone  is  changed  into  quicklime,  or  lime, 
as  it  is  commonly  called. 

Exercise  4.  Place  some  of  the  limestone  in  an  ignition 
tube  provided  with  a  suitable  delivery  tube  and  pass  into 
limewater  the  gas  which  is  given  off.  A. white  precipitate 
is  formed.  What  does  that  fact  indicate?  Review  the 
exercises  on  page  109. 

Let  us  understand  clearly  what  has  happened.  The 
chemical  name  of  limestone  is  calcium  carbonate.  Its 
formula  is  CaCOs.  The  heat  has  weakened  the  union 
between  the  different  elements  of  the  limestone,  and 
carbon  dioxid  has  been  driven  off.  All  the  carbon  and 


142  Science  for  Beginners 

part  of  the  oxygen  pass  off  into  the  air  as  carbon 
dioxid,  leaving  the  calcium  and  one  atom  of  oxygen 
behind  in  the  form  of  quicklime,  or  calcium  oxid. 

CaC03  ->  CaO  +   C02 

limestone   — >•  quicklime  +  carbon  dioxid 

How  to  write  a  chemical  story.  A  chemical  equation 
is  a  history  or  story  of  a  chemical  transaction.  It  is 
the  chemist's  way  of  telling  what  happens  when  a  chemi- 
cal change  takes  place.  An  important  point  to  remember 
in  writing  a  chemical  equation  is  that  all  cases  of  chemical 
action  follow  the  law  of  conservation  of  matter.  Hence, 
the  equation  must  show  what  has  become  of  every  atom 
that  entered  into  the  action.  We  may  think  of  a 
chemical  action  as  a  battle  and  the  atoms  as  the  soldiers ; 
but  after  the  chemical  battle  is  over  every  soldier  that 
entered  the  fight  is  still  on  the  field.  Can  you  explain 
what  becomes  of  all  the  atoms  when  limestone  is  heated  ? 

A  study  of  quicklime.  Use  the  quicklime  produced  in 
Exercises  3  and  4,  or  get  some  from  a  dealer.  It  must  be 
fresh  and  in  lumps ;  air-slaked  lime  will  not  do  for  your 
experiments.  Any  lumps  that  are  to  be  preserved  must 
be  kept  in  dry,  tightly  stoppered  bottles. 

Exercise  5.  Place  some  of  the  lime  in  a  dish  and  drop  some 
rainwater  or  distilled  water  slowly  upon  it.  Notice  the  hissing 
sound,  the  steam  which  rises,  and  the  heat  which  is  produced. 

The  fact  that  heat  is  produced  is  proof  to  the  chemist 
that  there  has  been  chemical  action  between  the  lime 
and  the  water.     The  story  can  be  told  in  this  way : 
CaO  +  H20  -*  Ca(OH)2 

lime     +    water  — *>  slaked  lime,  or  calcium  hydroxid 


The  Limestone  Story 


143 


carbon   dioxid 
to  form 


Exercise  6.  Continue  the  addition  of  water  to  the  lime 
used  in  the  last  exercise  until  most  of  the  lime  has  been 
dissolved.  Allow  the  solution  to 
settle  and  put  the  clear  liquid  into 
a  clean  bottle.  Stopper  the  bottle 
tightly  and  label  it  Limewater, 
or  Ca(OH)2. 

Manufacturing  limestone.  We 

produced  lime  by  driving  carbon 
dioxid  out  of  limestone  (Exer- 
cises 2  and  3) .  Then  we  added 
water  to  the  lime  and  formed  a 
compound  of  the  lime  which  dis- 
solved in  the  water  (Exercises  5  FIG.  84.  The 
and  6).  What  would  happen  if  unites  ^ the 

limestone. 

we  should  again  add  the  carbon 

dioxid  to  the  limewater  ?  This  you  have  already  done  in 
many  experiments,  and,  as  you  know,  a  white  precipitate 
is  formed.  This  precipitate  is  limestone;  the  carbon 
dioxid  and  the  lime  compound  reunite  and  form  fine 
particles  of  limestone  (shall  we  call  them  little  stones?) 
which  give  a  white  appearance  to  the  water. 

Ca(OH)2      +     C02     ->CaC03  +  H2O 

limewater  +  carbon  dioxid  — >  limestone     +    water 

Exercise  7.  Breathe  through  a  glass  tube  or  a  straw  into 
a  test  tube  of  limewater.  You  are  now  operating  a  limestone 
factory.  In  what  two  ways  could  you  again  break  up  this 
limestone  into  carbon  dioxid  and  lime? 

Now  review  Exercise  4.  In  one  test  tube,  the  lime- 
stone is  decomposed  and  the  carbon  Jioxid  is  given  off ; 


144  Science  for  Beginners 

in  the  second  tube  the  carbon  dioxid  unites  with  the 
limewater  to  recompose*  limestone.  In  the  one  tube 
you  were  breaking  up  limestone;  in  the  other  you 
were  making  it  again.  Do  you  know  how  lime  is  manu- 
factured and  what  happens  to  it  if  it  is  exposed  to  the  air  ? 

Chemical  changes  in  mortar  and  whitewash.  Slaked 
lime  mixed  with  sand  makes  mortar  for  plastering  and 
bricklaying.  When  mortar  is  exposed  to  the  air,  it 
gradually  takes  up  carbon  dioxid  from  the  air  and  the 
lime  in  it  is  changed  to  solid  limestone  again.  Slaked 
lime  with  water  is  used  for  whitewash.  This  takes  up 
carbon  dioxid  from  the  air  and  forms  a  thin  coating  of 
limestone  over  objects  that  are  whitewashed. 

Uses  and  forms  of  limestone.  Limestone  is  exten- 
sively used  in  the  manufacture  of  iron ;  millions  of  tons 
of  it  are  burned  each  year  to  produce  lime ;  it  is  ground 
and  spread  on  agricultural  lands  to  destroy  the  acid  in 
them;  and  when  ground  fine,  mixed  with  clay,  and 
burned,  it  forms  the  compound  known  as  "  Portland 
cement."  Some  limestones  contain  cracks  and  fissures* 
along  which  they  can  be  split.  Limestone  of  this  kind 
is  much  used  for  building  stone,  flagstones  for  sidewalks, 
and  other  purposes. 

Marble  is  a  limestone  which  is  crystallized,  compact, 
and  fine  grained.1  It  will  take  a  high  polish,  and  is 
used  for  statuary,  tombstones,  table  tops,  mantels,  and 
floors. 

In  some  countries  there  are  deposits  of  a  soft,  friable* 
limestone  which  is  known  as  chalk.  It  is  composed  of 
the  shells  of  small  animals.  What  is  the  difference 


The  Limestone  Story  145 

between  chalk  and  crayon?  Why  is  England  some- 
times called  "old  Albion"? 

Pearls  are  rounded  masses  of  limestone  found  on  the 
interior  of  oyster,  mussel,  and  other  bivalve*  shells. 
They  are  formed  of  mother-of-pearl,  —  the  same  sub- 
stance which  lines  the  inner  surface  of  the  shells.  Very 
small  parasitic  worms  infest  the  oyster  and  the  mussel, 
and  when  one  of  these  worms  dies  in  the  body  of  the 
animal  it  is  incased  in  mother-of-pearl.  A  French  writer 
has  said,  "  The  ornament  associated  in  all  ages  with 
beauty  and  riches  is  nothing  but  the  brilliant  sarcoph- 
agus* of  a  worm." 

Marl  is  a  soft  and  granular  form  of  carbonate  of  lime 
found  at  the  bottom  of  some  fresh-water  lakes  and  on 
their  shores.  It  is  generally  mixed  with  more  or  less 
clay. 

Deposits  of  marl.  In  the  northern  part  of  the  United 
States  there  are  thousands  of  fresh-water  lakes,  and  in 
the  waters  of  these  lakes  there  grows  a  small  plant 
(Chara*)  which  takes  limestone  out  of  the  water  and 
with  it  builds  a  crust  over  itself.  Where  these  plants 
have  been  growing  for  centuries,  there  have  been  formed 
from  their  skeletons  great  deposits  of  marl.  Animals, 
like  the  oyster,  that  build  shells  also  take  limestone  out 
of  the  water,  and  marl  deposits  may  be  formed  from 
beds  of  shells.  Marl  in  beds  of  great  thickness  is  found 
not  only  in  and  near  our  northern  lakes,  but  also  in  the 
valleys  of  some  of  our  large  rivers,  —  the  Mississippi, 
Missouri,  Colorado,  and  Alabama,  —  along  the  shores  of 
Chesapeake  Bay,  and  in  many  other  parts  of  the  United 


146  Science  for  Beginners 

States.  These  beds  are  of  great  value  for  the  manufacture 
of  Portland  cement. 

Exercise  9.  If  there  is  a  lake  near  you,  bring  up  material 
from  the  bottom.  If  this  is  white  after  drying,  it  is  probably 
marl.  Do  the  marl  deposits  extend  out  under  the  marsh 
land  near  the  lake  ?  If  there  are  marl  beds  of  any  kind  in  the 
vicinity,  bring  samples  of  them  to  school. 

Test  the  samples  with  acid.  A  good  marl  will  effervesce 
when  treated  with  an  acid.  Rub  a  little  of  the  marl  between 
the  fingers  and  also  take  some  upon  the  tongue.  If  it  feels 
"  gritty,"  it  is  probably  mixed  with  sand  and  would  not  be 
the  best  kind  for  making  cement. 

Measuring  the  amount  of  marl  in  a  deposit.  To  be 
profitable  for  cement  making,  a  marl  bed  should  be  of 
at  least  100  acres,  with  an  average  depth  of  from  15  to 
20  feet  of  good  marl.  In  case  you  have  found  what 
seems  to  be  a  good  marl  deposit,  you  may  be  interested 
in  learning  how  to  estimate  how  much  marl  is  avail- 
able. To  do  this  the  land  is  laid  off  in  squares  of 
10  rods  each  way,  and  two  facts  are  ascertained :  (i) 
the  depth  of  the  rock  or  soil  over  the  marl  (in  order  to 
estimate  correctly  the  cost  of  removing,  or  "  stripping 
off,"  the  soil),  and  (2)  the  depth  of  the  marl.  An  auger 
about  an  inch  and  a  half  in  diameter  and  attached  to  a 
long  rod  may  be  used  to  test  the  depth  of  the  marl. 
The  rod  may  be  made  of  three-quarter-inch  gas  pipe 
cut  into  pieces  5  feet  long  and  jointed  together.  A 
paper  laid  off  in  squares  will  serve  as  a  map  of  the  land 
that  is  being  tested.  As  each  hole  is  bored  a  record  of 
the  findings  is  entered  on  the  map. 


The  Limestone  Story 


147 


Clay  for  cement  making.  The  other  constituent  of 
Portland  cement  is  clay.  There  is  no  easy  way  by  which 
good  clay  can  be  determined,  and  specimens  must  be 
sent  to  some  competent*  chemist.  When  placed  upon 
the  tongue,  it  should  feel  smooth  and  "  soapy  "  but 
should  not  show  any  grit.  When  pure  clay  is  mixed 
with  water  and  then  dried,  it  becomes  very  hard.  The 
author,  when  a  boy,  made  very  good  marbles  in  this  way. 

For  what  purposes  is  Portland  cement  used?  How 
many  miles  of  cement  sidewalks  are  there  in  your  town  ? 
What  does  it  cost  per 
square  yard  to  build  such 
walks?  How  much  money, 
therefore,  is  invested  in 
such  walks  in  your  town  ? 

Caverns  in  limestone 
regions.  Limestone  is 
dissolved  by  water,  and 
in  limestone  regions  it  is 
not  uncommon  for  streams 
to  run  underground  in 
caverns  that  they  have 
made  for  themselves  in 
the  rocks.  The  great 
Mammoth  Cave  in  Ken- 
tucky and  the  beautiful 
Luray  Caverns  in  Virginia 
were  formed  in  this  way. 

In    Florida    larcre    under-     FlG'  8s'  Limestone  deposited  by  water 

trickling  down  the  side  of  the  Luray 

ground  rivers  reach  the     Caverns. 


148  Science  for  Beginners 

sea  through  channels  in  the  soft  limestone  of  which  a 
considerable  part  of  that  state  is  formed. 

Exercise  10.  Breathe  through  a  glass  tube  or  straw  into 
a  tube  of  limewater.  At  first  calcium  carbonate  is  precip- 
itated. Continue  breathing  carbon  dioxid  into  the  water. 
After  the  water  becomes  heavily  charged  with  carbon  dioxid, 
the  calcium  carbonate  is  dissolved  and  the  liquid  again  be- 
comes clear. 

Water  which  penetrates  deep  into  the  earth  takes 
up  carbon  dioxid,  and  this  greatly  increases  its  power 
to  dissolve  limestone  (page  67).  Can  you  explain  how 
the  sparkling  limestone  crystals  which  make  the  Luray 
Caverns  and  many  other  caverns  so  beautiful  are  formed  ? 

The  formation  and  occurrence  of  limestone.  Lime- 
stone composes  one  eighth  of  the  earth's  crust.  Some- 
times it  is  found  in  deposits  of  marl,  coral  rock,  or  chalk ; 
sometimes  in  massive  beds  hundreds  or  even  thousands  of 
feet  thick.  Where  did  this  limestone  come  from?  It 
is  laid  down  from  water  in  various  ways.  Animals  like 
the  oyster  and  other  mollusks  take  the  limestone  from 
the  water  of  the  sea  to  build  their  shells ;  the  coral  polyp 
builds  up  great  ledges  and  reefs  of  limestone  from 
materials  that  it  takes  from  the  sea ;  many  very  minute 
marine*  animals  build  shells  that  sink  to  the  bottom  on 
the  death  of  the  animals  and  slowly  form  layers  of  lime- 
stone; and  from  the  ocean's  waters  vast  amounts  of 
calcium  carbonate  are  precipitated  to  make  great  beds  of 
limestone  in  the  depths  of  the  sea.  In  time  part  of  this 
limestone  is  raised  to  form  land,  and  then  is  again  dis- 
solved and  carried  by  the  running  water  to  the  sea. 


CHAPTER   SIXTEEN 

A   FIELD    EXCURSION   FOR   MINERALS 

READ  the  first  part  of  this  chapter  over  carefully 
before  you  start  on  your  excursion ;  then  take  the  book 
with  you,  find  some  comfortable  place  to  sit  down,  and 
read  it  again. 

On  a  preceding  field  excursion  you  went  out  to  look 
for  limestone.  This  time  it  may  be  for  another  class  of 
minerals.  You  will  need  to  take  along  several  things : 
do  not  forget  your  eyes  —  you  will  need  to  have  them 
wide  open  at  every  step ;  you  will  need  an  old  knife, 
for  you  can  identify  minerals  by  their  hardness  more 
easily  than  by  any  other  quality ;  you  will  need  your  little 
bottle  of  hydrochloric  acid  in  order  to  note  its  action  on 
the  various  minerals  you  may  find ;  and  you  should  have 
a  hammer  and  a  small  piece  of  window  glass.  If  in 
addition  you  have  enthusiasm,  you  will  find  it  a  great 
pleasure  to  go  out  to  ask  questions  of  Mother  Nature. 
On  the  whole,  you  will  not  have  so  much  trouble  this 
time  to  find  what  you  want  as  you  had  in  the  excursion 
for  limestone,  although,  of  course,  the  difficulty  of  the 
search  depends  upon  the  particular  region  in  which  you 
live. 

Exercise  i.  Go  out  into  the  open  fields,  or  along  a  rail- 
road cut,  a  gravel  pit,  or  the  shore  of  a  lake.  Look  for 
minerals  answering  to  the  following  description : 

(1)  So  hard  that  they  cannot  be  scratched  with  a  knife; 
so  hard  that  the  sharp  edge  of  a  fragment  will  scratch  the 
window  glass. 

(2)  Sometimes  transparent  or  translucent,*  but  generally 
of  a  uniform  dull  color ;  brown,  yellow,  red,  or  gray.     Some- 

149 


150  Science  for  Beginners 

times  there  are  different  colors  in  rings  or  bands;  some- 
times the  mineral  looks  soft,  like  wax,  and  yet  is  very 
hard. 

(3)  When  broken  into  pieces,   showing  surfaces  that  are 
never  smooth  and  glistening.     If  you  are  told  that  frequently 
the  broken  surface  is  conchoidal,*  will  you  look  that  word  up 
and  see  what  is  meant  by  it? 

(4)  Generally  rounded  and   smoothed;    such   specimens 
are  often  found  as  pebbles. 

If  you  have  found  minerals  that  have  the  above 
properties,  you  have  doubtless  obtained  specimens  of 
what  is  known  by  the  general  name  of  quartz.  Quartz 
is  the  hardest  of  all  common  minerals,  and  if  you  find  a 
specimen  on  which  the  knife  leaves  a  dark  streak  of 
iron,  it  is  surely  quartz.  The  chemical  name  of  quartz 
is  silicon  dioxid  (SiO2).  It  is  a  compound  of  silicon, 
an  element  that  is  abundant  in  compounds  but  is  very 
rare  in  its  elementary  form.  Ordinary  sand  is  finely 
divided  quartz,  and  sandstone  is  particles  of  sand  bound 
together  by  some  cementing  substance. 

Exercise  2.  After  you  get  home  take  your  Bible  and 
read  the  twenty-first  chapter  of  Revelation.  Look  for  the 
minerals  that  are  mentioned  there  and  make  a- list  of  them. 
For  the  most  part  they  are  all  varieties  of  the  mineral  quartz. 
Look  up  their  proper  pronunciation  and  interesting  facts 
concerning  them  in  the  dictionary  or  encyclopedia. 

It  is  desirable  to  have  access  to  a  good  collection 
of  quartz.  No  other  mineral  is  found  in  so  many 
beautiful  forms  as  this.  Some  of  the  more  common  forms 
are  described  below,  and  in  the  list  you  may  find  some  of 
the  specimens  that  you  have  gathered.  Bear  in  mind 


A  Field  Excursion  for  Minerals 


FIG.  86.     "Crystal  gazing."     It  was  formerly  believed  that  an  alchemist  could 
read  the  future  in  his  crystal  globe. 

that  every  mineral  in  the  following  list  is  simply  a  variety 
of  quartz,  and  that  each  one  possesses  the  qualities  that 
you  looked  for  in  making  your  collection. 

Rock  crystal.  Pure  pellucid*  quartz.  When  the 
crystals  are  separate,  they  may  be  known  by  their  form, 
which  is  almost  always  that  of  a  six-sided  prism  ter- 
minated with  six-sided  pyramids  (Fig.  52).  The  an- 
cients applied  the  word  crystal  to  this  mineral;  it  is 
from  a  Greek  word,  krustallos,  meaning  ice.  In  spite 
of  its  hardness,  pure  specimens  of  quartz  are  often  cut 
into  jewelry.  Rock  crystal  is  also  used  for  optical  in- 
struments and  spectacle  glasses.  Even  in  ancient  times 
it  was  cut  into  cups  and  vases.  Nero,*  on  hearing  of  the 
revolt  that  caused  his*  ruin,  is  said  to  have  dashed  to 
pieces  two  cups  made  of  this  material.  It  was  formerly 
believed  that  certain  persons  could  read  the  future  by 
steadfastly  gazing  into  a  globe  cut  from  pure  rock 


152  Science  for  Beginners 

crystal,  and  "  crystal  gazing  "  is  still  sometimes  practiced 
as  a  sport. 

"  Brazilian  pebbles  "  and  "  Alaska  diamonds  "  are 
merely  crystalline  quartz. 

Amethyst.  Purple  or  bluish  violet.  This  is  one  of 
the  most  beautiful  varieties  of  quartz  and  is  highly 
esteemed  as  a  gem. 

Rose  quartz.  Pink  or  rose  colored.  Does  not  usually 
crystallize.  Not  much  used  for  ornamental  purposes, 
as  the  color  fades. 

False  topaz.  Light  yellow  crystal.  Often  cut  and 
set  for  real  topaz,  which  is  quartz  combined  with 
aluminum  and  fluorin. 

Smoky  quartz.  Crystals  of  a  smoky  tint;  color 
sometimes  so  dark  as  to  be  nearly  black. 

Milky  quartz.  Milky  white,  nearly  opaque,  and  of 
common  occurrence.  Has  often  a  greasy  luster.* 

Chalcedony.  Translucent,  with  a  waxy  luster,  looking 
as  if  it  could  be  cut  with  the  finger  nail.  It  often  fills 
cavities  in  other  rocks.  Chalcedony  containing  minute 

mossy  patches  of  a  darker  color 
is  moss  agate. 

Agate.  A  semipellucid,*  un- 
crystallized  variety  of  chalcedony 
which  has  various  colors  in  the 
same  specimen.  The  colors  are 
arranged  in  bands  or  there  may 

FIG.  87.    A  cameo.  .  .         „ 

be  a  cloudy  effect. 

Chrysoprase.  Apple-green  chalcedony;  colored  by 
nickel. 


A  Field  Excursion  for  Minerals 


153 


Carnelian.  Bright  red 
chalcedony,  of  a  rich  clear 
tint.  Much  used  in  jew- 
elry. 

Onyx.  A  variety  of 
agate  in  which  the  colors 
are  arranged  in  flat,  par- 
allel layers.  Usually  one 
of  the  colors  is  white; 
and  when  an  emblem  or 
figure  is  carved  out  of  one 
color  with  the  other  as  a 
base,  a  cameo  is  produced. 

Flint.  Dark  shades  of 
smoky  gray,  brown,  or 
even  black,  translucent  on 
thin  edges,  breaking  with 
sharp  edges  and  a  con- 
choidal  surface.  Indian 
arrowheads  are  made  from 
this  variety  of  quartz. 

Jasper.    A  dull  opaque 
red,  brownish,  or  greenish 
quartz.    Can  be  highly  polished.    It  will  be  quite  easy  to 
find  good  specimens  of  jasper  in  any  of  the  Northern  states. 

Bloodstone  or  Heliotrope.  Deep  green,  slightly 
translucent,  containing  spots  of  red  due  to  a  small 
percentage  of  clay  and  iron  oxid.  In  the  royal  collection 
in  Paris  is  a  bust  of  Christ  cut  from  this  stone  in  such 
a  manner  that  the  red  spots  appear  as  drops  of  blood. 


U.  S.  Geological  Survey 
FIG.  88.    Silicified  tree  trunk  in  the 
Yellowstone  National  Park. 


154  Science  for  Beginners 

Opal.     Colors  —  white,    yellow,    red,    brown,    green, 
blue,  and  gray.     A  good  specimen  will  show  a  rich  play 
of  colors  when  turned  in  the  hand. 

Silicified  wood.  Petrified*  wood  often 
consists  of  quartz  which  has  taken  the 
place  of  the  original  particles  of  the 
wood. 

Quartz  in  the  earth's  crust.  One 
FIG  &r~fc~JDiagram  more  statement  will  show  the  impor- 
showing  the  amounts  tance  of  the  substance  which  we  have 

of  different  elements  in      .          studied.      The  CHlSt  of   the  earth, 
the  earth's  crust  J  %  .  . 

as  we  know  it,  is  1 8  or  20  miles  thick. 
Three  quarters  of  it  is  made  of  either  pure  quartz 
or  its  compounds.  If  we  should  represent  by  a  circle 
the  materials  of  which  the  crust  of  the  earth  is  com- 
posed (Fig.  89),  one  half  of  the  circle  would  represent 
oxygen ;  for  one  half  of  the  outer  layers  of  the  earth  is 
oxygen.  One  half  of  the  remaining  half,  or  one  quarter 
of  the  whole,  is  the  element  known  as  silicon.  But 
the  silicon  is  combined  with  oxygen  to  form  quartz,  so 
that  the  greater  portion  of  the  surface  layers  of  the  earth 
is  composed  of  the  mineral  which  has  been  the  object 
of  this  study.  One  third  of  the  remaining  fourth  of  the 
crust  of  the  earth  is  the  metal  calcium,  which  is  most 
often  combined  with  carbon  and  oxygen  to  form  lime- 
stone. All  other  chemical  elements,  as  is  shown  by  the 
diagram  (Fig.  89),  form  but  a  small  proportion  of  the 
outer  layers  of  the  earth. 


CHAPTER   SEVENTEEN 

LOOKING  FOR  ROCKS 


FIG.  go. 

EXAMPLES  of  minerals  have  been  studied  in  the  lime- 
stone and  quartz.  These  and  all  other  minerals  have  a 
definite  chemical  composition.  Thus  limestone  is  cal- 
cium carbonate  (CaCOa),  agate  is  silicon  dioxid  (SiO2), 
diamond  is  crystallized  carbon  (C),  the  ruby  and  the 
sapphire  are  oxids  of  aluminum  (AljOt),  iron  ore  is  an  oxid 
of  iron  (Fe2O3),  common  salt  is  sodium  chlorid  (NaCl). 

Rocks,  on  the  other  hand,  are  mixtures  of  two  or 
more  minerals.  They  are  to  be  recognized,  usually, 
by  the  fact  that  to  the  eye  they  present  various  colors 
or  differences  in  structure  in  different  places  in  the 
rock.  They  are  not  homogeneous,*  as  the  scientists 

155 


156 


Science  for  Beginners 


FIG.  91.     The  structure  of  granite. 

would  say.  What  word  should  you  apply  to  them  if 
they  are  not  homogeneous  ? 

Granite.  One  rock  with  which  nearly  every  one  has 
an  acquaintance  is  granite.  This  is  a  mixture  of  three 
minerals :  quartz,  feldspar,  and  mica.  It  may  be  seen 
in  the  stone  fences  and  bowlders  which  are  to  be  found 
everywhere  in  all  the  states  north  of  a  line  approxi- 
mately following  the  Ohio  and  Missouri  rivers.  Coarse 
granite  may  easily  be  recognized  by  the  black  or  golden 
flakes  of  mica  embedded  in  a  mixture  of  white  or  gray 
quartz  and  flesh-red  or  pink  feldspar.  Look  for  three 
colors,  all  more  or  less  intermingled,  —  dark  specks 
and  scales  on  a  grayish  and  pinkish  background. 

Quartz.  You  have  already  studied  quartz  and  will 
be  able  to  recognize  it  by  its  peculiar  qualities.  In 
granite  its  color  is  usually  white  or  gray ;  it  is  so  hard 
that  it  will  scratch  glass  and  cannot  itself  be  scratched 
with  a  knife.  In  the  granite  the  quartz  mineral  is 
generally  in  rounded  grains  or  pebbles.  Sometimes 
these  are  so  closely  crowded  together  that  their  outlines 


Looking  for  Rocks  157 

cannot  easily  be  separated  from  the  other  minerals  in 
the  rock.     In  coarse  granite  this  can  easily  be  done. 

Feldspar.  Is  there  a  light-colored,  pinkish,  reddish,  or 
flesh-colored  part  of  the  granite,  which  can  be  scratched 
with  a  knife,  although  possibly  with  some  difficulty  ?  It 
is  probably  feldspar.  Quartz  will  scratch  feldspar ;  but 
feldspar  will  not  scratch  quartz.  If  there  is  difficulty 
in  deciding  whether  a  given  mineral  is  feldspar  or  quartz, 
there  are  several  ways  to  find  out  which  it  is.  First  ex- 
amine it  as  to  its  luster,  its  power  to  reflect  the  light. 
Quartz  looks  like  broken  glass;  feldspar  has  a  pearly 
luster.  Compare  your  specimen  with  a  piece  which  you 
know  to  be  pure  quartz. 

Next,  notice  whether  the  mineral  shows  anywhere  a 
tendency  to  break  into  flat  surfaces  along  two  directions 
that  are  nearly  at  right  angles  to  each  other.  Quartz 
never  presents  flat  surfaces  or  faces ;  feldspar  presents 
two  such  faces.  Again,  these  flat  surfaces  of  the  feld- 
spar, when  held  in  the  sun,  reflect  the  light.  By  this 
sign  we  can  be  fairly  sure  of  feldspar.  Gather  a  number 
of  specimens,  choose  the  coarsest  ones,  and  do  not  be  dis- 
couraged if -you  cannot  at  once  and  clearly  distinguish 
between  quartz  and  feldspar. 

Mica.  Usually  mica  is  of  a  dark  or  black  color  and 
may  be  split  into  small,  flat  scales  which  reflect  the 
light  and  glisten  in  the  sun.  If  the  surfaces  are  brilliant, 
the  scales  are  generally  elastic ;  but  sometimes  we  find 
that  they  have  lost  their  elasticity. 

Mica  is  found  in  some  places  in  large  masses  that  will 
split  into  thin,  tough,  flexible,  elastic  scales.  In  that 


158  Science  for  Beginners 

0 

form  it  is  extensively  used  in  stove  doors.  Ask  the 
hardware  man  for  some  scraps  of  mica. 

Iron  pyrites.  Sometimes  the  granite  is  in  the  process 
of  being  broken  up  by  the  action  of  water,  especially 
when  the  water  freezes.  This  is  often  due  to  the  pres- 
ence of  small  particles  of  iron  pyrites,  or  "  fool's  gold," 
as  it  is  sometimes  called,  which  is  a  compound  of  iron 
and  sulfur.  The  action  of  the  oxygen  of  the  air  renders 
pyrites  somewhat  soluble  in  water,  and  granite  that 
contains  it  is  sometimes  quite  broken  up  by  exposure  to 
the  weather.  Pyrites  is  easily  recognized,  as  it  shines 
like  gold  when  held  in  the  sun. 

Sometimes  you  may  be  curious  to  know  whether  these 
shining  golden  particles  are  not  really  gold.  Pure  gold 
rarely  occurs  in  masses  large  enough  to  be  seen  by  the 
unaided  eye,  and  a  chemical  test  that  will  distinguish 
iron  pyrites  from  gold  is  easily  made.  Strong  hydro- 
chloric acid  applied  to  the  pyrites  will  give  the  odor  of 
hydrogen  sulfid  (H2S),  —  the  well-known  odor  of  de- 
caying eggs.  This  acid  has  no  effect  upon  pure  gold. 
Heating  the  pyrites  over  a  hot  flame  will  give  the  odor 
of  sulfur  dioxid,  —  the  familiar  odor  of  burning  sulfur. 

Occurrence  and  uses  of  granite.  Much  of  the  deeper 
part  of  the  earth's  crust  is  granite,  and  many  vast  moun- 
tain chains  are  granite.  It  is  one  of  our  hardest  and 
most  enduring  rocks  except  when  it  contains  other 
minerals  besides  quartz,  feldspar,  and  mica,  such  as  the 
iron  pyrites  mentioned  above.  Notwithstanding  the 
difficulty  of  working  it,  granite  is  used  for  monuments 
and  building  purposes,  because  it  so  well  withstands 


Looking  for  Rocks 


159 


U.  S.  Geological  Survey 
FIG.  92.    A  granite  mountain  in  Georgia. 

the  crumbling  hand  of  time.  In  cemeteries  may  be 
seen  polished  granite  monuments  which  show  clearly 
the  structure  of  the  rock. 

Other  rocks.  The  rocks  which  make  up  the  earth's 
crust  are  of  many  different  kinds.  Besides  granite, 
which  we  have  studied,  sandstones,  shales,  and  volcanic 
rocks  cover  great  portions  of  the  surface  of  the  earth. 
You  will  observe  and  study  these  with  more  interest  if 
you  understand  how  they  are  formed.  They  are  divided 
according  to  their  origin  into  two  great  classes,  igneous* 
and  sedimentary*  rocks. 

Igneous  rocks.  Granite  is  an  igneous  rock.  It  is  a 
part  of  the  original  molten  matter  of  which  the  earth  was 


i6o 


Science  for  Beginners 


U.  S.  Geological  Survey 
FIG.  93.    A  lava  field  in  the  Hawaiian  Islands. 

formed.  Volcanic  rocks  also  are  igneous  rocks;  they 
are  formed  from  lava  which  has  been  poured  forth  from 
volcanoes  and  which,  in  ages  past,  flowed,  in  some 
parts  of  the  earth,  through  cracks  in  the  earth's  crust. 
Much  of  the  surface  of  a  number  of  our  Western  states 
is  covered  with  volcanic  rock ;  many  of  the  islands  of 
the  Pacific  Ocean  (the  Aleutian  Islands,  Japan,  the 
Philippines,  the  Hawaiian  Islands,  and  many  others) 
have  been  built  by  volcanoes;  and  a  large  part  of 
southern  Idaho  is  covered  by  a  sheet  of  lava  which  welled 
up  through  a  great  fissure  along  the  mountains  on  the 
eastern  border  of  the  state  and  flowed  westward  in  a 
vast  flood.  Another  example  of  igneous  rocks  is  found 
in  the  famous  Palisades  of  the  Hudson  River.  These 
were  formed  from  material  that  came  up  through  a  crev- 
ice in  the  earth  and  crystallized  into  great  columns  as 


Looking  for  Rocks 


U.  S.  Geological  Survey 
FIG.  94.    The  Palisades  of  the  Hudson. 

it  cooled.  Igneous  rocks  cover  about  one  tenth  of  the 
surface  of  the  earth,  and  wherever  there  are  sedimentary 
rocks,  igneous  rocks  underlie  them. 

Sedimentary  rocks.  In  any  part  of  the  United  States 
it  is  easy,  after  a  long  and  heavy  rain,  to  find  places 
along  the  banks  of  creeks  or  rivers  where  the  water  has 
overflowed  the  land.  In  time  the  flood  will  recede  or 
seep  into  the  earth,  and  after  that  has  taken  place  you 
will  see  a  thin  film  of  muddy  slime  covering  the  surface 
of  the  ground.  Thousands  of  people  who  live  on  the 
lowlands  bordering  the  Ohio  River,  for  example,  look 
with  great  anxiety  to  the  time  when  the  spring  rains  will 
melt  the  accumulation  of  the  snows  of  winter.  The  river 
then  overflows  its  natural  banks  and  the  muddy  water 
covers  every  place  where  it  stands  —  streets,  cellars, 


1 62  Science  for  Beginners 

and  sometimes  the  '.houses  —  with  a  thick  deposit 
of  mud.  Where  did  the  mud  come  from?  Evidently 
from  the  land  lying  on  the  hills  and  high  ground  along 
the  borders  of  the  creek  or  river.  All  through  the 
long  period  of  time  during  which  this  stream  has  ex- 
isted, soil  has  been  transferred  from  the  hillsides  to  the 
valley. 

Suppose  this  has  been  going  on  along  our  rivers  for 
thousands  of  years.  You  can  understand  how  in  the 
course  of  time  a  tremendous  amount  of  material  has  in 
this  way  been  transferred  to  the  lower  land  and  deposited 
at  the  mouths  of  rivers  in  the  sea  (page  170).  This 
is  one  of  nature's  methods  of  making  land,  and  you 
can  find  proof  everywhere  that  lakes  and  the  ocean 
at  the  mouths  of  rivers  are  slowly  filling  up,  leaving 
finally  a  low,  level  deposit  of  soil.  What  is  the  deposit 
of  land  at  the  mouth  of  a  river  called  ? 

The  process  by  which  the  hills  and  banks  of  streams 
are  worn  down  is  called  erosion.*  The  material  that  is 
carried  by  the  water  is  called  sediment.*  The  process 
of  depositing  this  material  is  called  sedimentation. 

It  is  not  difficult  for  us  to  understand  how  the  soft 
earth  is  finally  changed  to  solid  rock.  We  have  only 
to  take  into  account  the  element  of  time.  The  time  that 
the  rivers  of  the  earth  have  been  at  work  has  been  long, 
—  many  millions  of  years,  —  so  that  inevitably  some  of 
the  layers  of  sediment  that  were  first  laid  down  became 
pressed  upon  by  thousands  of  tons  of  deposits  above 
them.  This  pressure,  together  with  the  effect  of  the 
internal  heat  of  the  earth,  finally  compacted  the  sedi- 


Looking  for  Rocks  163 


FIG.  95-    Stratified  rock. 

ment  into  solid  rocks.  Why  are  these  rocks  called 
"  sedimentary  rocks  "? 

The  material  that  is  washed  down  by  streams  is  depos- 
ited in  layers,  and  when  the  sediment  hardens  the  layers 
may  still  be  seen.  These  are  called  strata  (singular, 
stratum) ;  the  rocks  are  said  to  be  stratified.  Such 
stratified  soil  and  rocks  may  often  be  seen  in  railroad 
cuts,  gravel  pits,  or  stone  quarries,  or  stratification 
may  be  observed  by  cutting  through  the  layers  of 
material  that  have  been  deposited  along  the  course  of 
a  stream. 

Fossils.  Any  shells  or  skeletons  of  animals  or  the 
remains  of  plants  that  became  buried  in  the  mud  and 
their  forms  pressed  into  the  rock  as  it  was  being  formed, 
are  known  as  fossils  (Fig.  88).  In  certain  regions  you 
may  easily  find  in  the  stratified  rocks  the  remains  of 
animals  that  lived  ages  ago.  The  fossils  of  the  gigantic 
animals  that  roamed  the  earth  millions  of  years  before 
man  made  his  appearance  are  one  of  the  great  sights 
that  a  modern  museum  offers. 


164  Science  for  Beginners 

Sandstones.  Sandstones  are  good  examples  of  sedi- 
mentary rocks  formed  from  the  wastes  of  such  rocks  as 
granite.  By  the  action  of  the  air  and  moisture,  together 
with  alternating  freezing  and  thawing,  the  feldspar  is 
changed  to  clay  and  washed  away  to  form  soil.  The 
quartz  is  left  as  sand  and  is  washed  into  the  sea  or  into  a 
lake,  where  it  spreads  out  in  layers.  Then  the  grains 
of  sand  are  cemented  together  by  some  mineral  like 
limestone  that  is  deposited  from  the  water.  In  this  way 
great  beds  of  sandstone  are  formed.  Red  sandstone  is 
cemented  together  with  oxid  of  iron,  and  because  the 
cement  is  not  affected  by  the  oxygen  of  the  air  this  kind 
of  sandstone  makes  a  most  durable  building  material. 
Why  is  iron  oxid  not  attacked  by  oxygen? 

Shale.  When  the  clay  and  other  fine-grained  sedi- 
ment which  is  carried  by  rivers  and  smaller  streams  is 
deposited,  the  rocks  formed  from  them  are  known  as 
shale  and  slate.  Shales  are  generally  gray  to  black  in 
color,  but  sometimes  of  dull  greenish,  purplish,  reddish, 
or  other  shades.  Often  they  split  into  very  fine  layers. 
When  shale  is  weathered,*  a  clay  soil  is  formed. 

Slates  are  dark,  fine-grained,  and  hard,  and  split 
very  evenly.  The  best  quality  of  slates  are  sometimes 
split  into  roofing  slate  or  writing  slate. 

Is  limestone  an  igneous  or  a  sedimentary  rock? 


CHAPTER  EIGHTEEN 

THE  SOIL 


Go  out  into  an  open  field, 
stand  still,  and  ask  yourself 
what  it  is  you  are  standing 
upon.  The  most  evident 
answer  you  could  make  is, 
"  I  am  standing  upon  the 
earth  "  ;  you  might  say,  "  I 
am  actually  in  contact  with 
Mother  Earth."  If  you  said 
old  Mother  Earth,  your  ex- 
pression would  not  be  con- 
sidered disrespectful,  for  the 
earth  is  very  old.  Some  day 
you  will  study  geology,  that 
science  which  deals  with  the 
earth  as  a  whole,  its  origin, 
its  history  through  the  count- 
less millions  of  years  which 
elapsed  before  man  came  to 
live  upon  it,  its  age,  and  some- 
thing of  its  future  destiny. 


FIG.  96. 


But  without  waiting  for  that  time,  you  ought,  here  and 
now,  to  have  some  general  ideas  concerning  the  earth. 
The  horizon.  There  is  the  horizon,*  circular  in  form 
and  usually  seeming  to  be  higher  than  the  place  where 
you  are  standing.  You  will  recall,  in  this  connection, 
the  facts  learned  in  geography  concerning  the  shape  of 
the  earth,  the  shadow  of  the  earth  on  the  moon  at  the 

165 


i66 


Science  for  Beginners 


FIG.  97.    Why  do  the  vessels  in  the  distance  disappear  from  sight? 

time  of  a  lunar  eclipse,  the  appearance  of  ships  as  they 
go  out  from  or  come  into  a  harbor  on  the  shore  of  the 
ocean,  and  the  experiences  of  men  who  have  traveled 
around  the  earth.  Call  to  mind  again  the  figures  given 
concerning  the  size  of  the  earth,  its  diameter,  and  its 
circumferences,  equatorial  and  polar.  Do  not  make 
this  review  in  the  house  but  out  of  doors.  While  you 
are  doing  this,  do  not  think  of  your  textbook,  but  rather 
'think  of  the  earth  itself. 

How  soils  are  formed.  Another  answer  might  be 
made  to  the  question  as  to  what  it  is  you  are  standing 
upon.  You  could  reply,  "  I  am  standing  on  the  soil," 
and  this  answer  might  suggest  questions  as  to  what  soil 
is  and  where  it  comes  from. 

All  soils  are  formed  by  the  breaking  down  of  the  solid 
rock  that  forms  the  crust  of  the  earth.  This  process  is 
going  on  all  the  time,  now  as  in  ages  past.  By  the  freez- 


The  Soil  167 

ing  and  thawing  of  the  water  that  finds  its  way  into  cracks 
and  crevices  of  rocks ;  by  chemical  action  of  the  oxygen 
of  the  air  ;  and  by  the  work  of  water,  winds,  and  plants, 
the  rocks  are  broken  and  crumbled  into  fine  particles 
that  we  call  the  soil. 

How  soils  are  classified.  Soils  are  classified  into 
three  principal  types,  according  to  their  origin.  These 
are  residual  soils,  or  soils  that  have  not  been  moved 
from  where  they  were  formed ;  alluvial  soils,  or  soils 
washed  down  and  deposited  by  water ;  and  drift,  or 
glacial  soils,  which  have  been  transported  in  some  cases 
for  many  miles  by  flowing  sheets  and  streams  of  ice. 

Soils  formed  and  deposited  by  glaciers.  From  New 
England  to  the  Missouri  River,  and  from  Hudson  Bay  to 
the  Ohio  River,  the  soil  in  most  places  is  a  bed  of  loose 
material  consisting  chiefly  of  sand,  gravel,  small  stones, 
and  clay.  This  material,  down  to  the  solid  rock,  which 
exists  everywhere  below  the  soil,  is  called  the  drift.  For  a 
proper  understanding  of  the  drift,  we  must  again  consult 
geology  and  there  learn  the  history  of  the  earth  through 
the  Glacial  Period.  As  preparatory  to  this,  we  may  re- 
view that  part  of  physical  geography  which  treats  of 
glaciers  and  the  work  they  are  now  doing  in  moving  earth 
and  rocks  from  higher  to  lower  altitudes. 

The  glacial  age.  By  proofs  which  cannot  be  given 
here,  geologists  are  able  to  show  that  at  some  time  before 
man  appeared  on  the  earth,  the  region  that  is  now  the 
northern  part  of  the  United  States  was  covered  with  a 
mass  of  ice,  or  vast  glacier,  and  not,  as  it  is  in  this  age, 
with  verdure  and  magnificent  forests.  This  sheet  of  ice 


i68 


Science  for  Beginners 


U.  S.  Geological  Survey 
FIG.  98.     Glacial  bowlders  in  a  field  in  Maine. 

moved  slowly  downward  from  the  north,  tearing  the 
rocks  from  their  beds  and  carrying  with  it,  frozen  into 
its  substance,  all  the  earth  and  loose  stones  lying  in  its 
path.  By  the  movement  of  the  glacier,  these  stones 
were  not  only  worn  and  smoothed  themselves,  but  they 
also  helped  to  break  up  the  rock  beneath  into  clay  and 
sand.  Thus  in  this  far-off  time  we  find  one  explanation 
of  the  presence  of  the  rocks  and  bowlders  which  cover 
the  greater  part  of  our  country  north  of  the  Ohio  and 
the  Missouri  rivers. 

The  drift.  In  brief,  then,  the  glacial  drift  consists  of 
earth  and  fragments  of  rocks,  more  or  less  finely  ground, 
which  were  broken  off  from  the  solid  rock  by  the  great 
glaciers  of  the  Glacial  Period  and  were  brought  by  that 
agency  from  the  north  to  the  regions  farther  south. 
Some  of  them  were  torn  from  rock  beds  and  ledges 


The  Soil  169 

hundreds  of  miles  north  of  where  they  now  lie,  as  is 
shown  by  the  material  of  which  they  are  composed. 
Afterwards,  when  the  great  glacier  melted,  there  was  the 
further  action  of  running  water,  the  result  of  which  was 
the  spreading  of  loose  material  over  hills  and  valleys  and 
the  prairie  region  of  our  country. 

The  thickness  of  the  glacial  drift  has  been  carefully 
measured  in  different  parts  of  the  United  States  and  has 
been  found  to  vary  from  a  few  inches  to  400  or  500 
feet.  It  is  generally  thicker  in  the  valleys  than  on 
higher  land,  so  that  almost  all  the  valleys  in  the  drift 
regions  are  more  or  less  filled  with  drift  gravel,  sand,  or 
clay. 

Exercise  i.  If  you  live  in  the  drift  region,  ascertain  how 
many  wells  in  your  locality  go  down  to  the  solid  rock.  In 
this  way  you  may  gain  a  clear  idea  of  the  depth  of  the  drift 
in  the  region  in  which  you  live. 

Alluvial  soil.  In  other  parts  of  the  United  States, 
especially  on  the  Atlantic  coastal  plain  from  New  Jersey 
southward,  on  the  lowland  north  of  the  Gulf  of  Mexico, 
and  on  a  wide  area  along  the  Mississippi  River  and  its 
tributaries  nearly  as  far  north  as  St.  Louis,  the  soil  is 
alluvial.  Century  after  century  the  streams  that  flow 
through  these  and  other  regions  have  been  washing  down 
soil  from  the  mountains  and  high  parts  of  the  continent 
and  depositing  it  along  their  valleys  and  at  their  mouths. 
Alluvial  soil  can  be  found  along  almost  any  stream,  and 
the  soils  of  many  fertile  regions,  like  the  valleys  of  the 
Nile  and  of  the  Ganges,  have  been  transported  and  laid 
down  in  this  manner  by  streams.  James  D.  Dana,  the 


170  Science  for  Beginners 

geologist,  says,  "  The  average  amount  of  sediment  an- 
nually carried  to  the  borders  of  the  Gulf  of  Mexico  by  the 
Mississippi  River  has  been  stated  to  be  812,500,000,000 
pounds,  or  enough  to  make  a  pyramid  a  square  mile  at 
the  base  and  over  700  feet  in  height."  The  material  is 
deposited  about  the  mouth  of  the  river,  and  is  gradually 
extending  the  land  farther  into  the  Gulf.  The  fine 
sediment  of  rivers  settles  much  more  rapidly  in  salt 
water  than  in  fresh,  and  that  is  one  reason  why  this 
material  is  prevented  from  being  carried  off  to  the  deep 
ocean. 

Exercise  2.  Hunt  for  examples  of  alluvial  soil  and  learn 
to  recognize  it  as  such.  In  most  regions  alluvial  deposits  can 
be  found  in  the  bends  of  streams. 

Residual  soils.  Most  of  the  people  whose  homes  are 
in  the  western  part  of  the  United  States  or  in  the  higher 
parts  of  the  South  live  on  residual  soil.  In  the  process 
of  decay,  part  of  the  material  of  which  the  rocks  are 
composed  is  dissolved  out  of  them  and  carried  away,  and 
the  soil  is  composed  of  those  parts  of  the  rock  which 
remain.  The  character  or  kind  of  residual  soil  depends 
on  the  materials  of  which  the  original  rocks  were  com- 
posed and  from  which  the  soil  was  made.  Sandstone 
and  pulverized  granite  make  sandy  soils;  limestones, 
feldspar,  and  shales  give  clay  soils. 

Exercise  3.     Find  examples  of  rock  changing  to  soil. 

An  agricultural  classification  of  soil.  From  an  agri- 
cultural standpoint,  soils  are  classified  as  sand^  clay, 
and  loam.  Sand  is  composed  of  rather  coarse  particles 


The  Soil 


171 


FIG.  99.     Testing  the  water-holding 
capacity  of  soils. 


and  clay  chiefly  of  very 
fine  particles,  while  on  the 
average  the  particles  of 
loam  are  finer  than  sand 
and  coarser  than  clay. 

Exercise  4.  Press  moist 
sand  together  in  the  hand. 
Do  the  particles  cohere*  ? 
Press  an  equal  amount  of 
clay.  Do  the  particles  co- 
here? Do  they  adhere*  to 
your  hand  ?  Test  a  loam  soil 
in  the  same  way.  A  loam  soil  is  more  sticky  than  sand  and 
less  sticky  than  clay. 

According  to  the  fineness  of  the  particles  of  which 
they  are  composed,  the  soils  of  our  country  have  been 
classified  by  the  United  States  Department  of  Agri- 
culture into  more  than  400  types,  ranging  "from  coarse 
gravel  to  very  fine  clay.  Certain  crops  do  well  on  one 
kind  of  soil  and  other  crops  flourish  on  soil  of  a  different 
type;  so  to  a  considerable  degree  the  success  of  the 
farmer  depends  on  how  well  he  suits  his  crops  to  his  land. 

The  water-holding  capacity  of  soils.  Plants  take  up 
water  through  their  roots,  and  one  of  the  important 
questions  about  an  agricultural  soil  is  the  amount  of 
water  it  will  hold.  By  the  following  experiment  we  can 
determine  the  water-holding  capacity  of  different  soils  : 

Exercise  5.  Take  three  tin  cans  of  equal  size;  make  a 
number  of  fine  holes  in  the  bottom  of  each  for  drainage. 
Spread  out  and  dry  on  papers  sand,  clay,  and  loam ;  fill  a 


172 


Science  for  Beginners 


can  with  soil  of  each  kind.  Weigh  the  cans  and  their  con- 
tents, record  the  weights,  and  then  set  the  cans  in  water 
nearly  to  the  top  and  let  them  stand  overnight.  The  next 
morning  take  the  cans  out  of  the  water  and,  after  they  have 
drained  thoroughly,  reweigh  them.  Which  can  has  gained 
most  in  weight? 

The  heat-absorbing  capacity  of  soils.  Few  seeds  will 
germinate  at  a  temperature  below  50  degrees,  and  the 
roots  of  many  plants  do  not  grow  well  in  a  cold  soil.  Test 
the  heat-absorbing  capacity  of  sand  and  clay  by  the  fol- 
lowing experiment : 

Exercise  6.  Provide  two  baking  tins.  Fill  one  with 
moist  sand  to  the  depth  of  3  inches  and  the  other  with  moist 
clay  to  the  same  depth.  Let  them  stand  in  the  same  room 
until  their  temperature,  as  shown  by  the  thermometer,  is 
the  same.  Place  them  on  the  stove  or  radiator  where  they 
will  heat  quite  slowly.  Take*  the  temperature  of  each  soil 
at  equal  intervals  of  time,  carrying  on  the  observation  while 
the  temperature  is  increasing  and,  after  the  pans  have  been 
removed  from  the  fire,  until  their  temperatures  are  again  the 
same.  Tabulate  your  observations. 


TIME  IN 
MINUTES 

CLAY 

SAND 

Temperature 

Temperature 

Rising 

Falling 

Rising 

Falling 

'•'•    "' 

The  Soil  173 

Which  soil  warms  up  more  rapidly?  Which  retains 
its  heat  longer  ?  Examine  again  the  results  you  secured 
in  Exercise  5.  Do  you  see  any  reason  for  the  results  you 
got  in  Exercise  6?  Would  a  sandy  or  a  clay  soil  be 
better  for  an  early  spring  garden? 

Vegetable  matter  in  the  soil.  If  the  uppermost 
layer  of  the  soil  be  examined,  it  will  be  seen  that  it  is  of 
darker  color  than  the  soil  below  and  evidently  contains 
something  besides  mere  particles  of  rocks.  Go  to  some 
railroad  cut  or  "sand  bank"  and  observe  this  fact.  The 
color  is  darkest  and  the  depth  of  the  soil  is  greatest 
in  places  where  most  vegetable  material  has  decayed ; 
as,  for  example,  in  forests  where  leaves  accumulate  and 
decay  from  year  to  year,  or  where  grasses  or  mosses  grow 
luxuriantly  and  decay,  as  in  marshes  and  swamps. 
Notice  also  that  the  lightest-colored  soil  is  found  in  places 
where  the  least  vegetation  has  decayed  —  on  dry  knolls 
and  in  situations  where  the  bed  rock  comes  near  the 
surface.  We  may  thus  conclude  from  our  observations 
that  the  soil  is  made  darker  by  the  decayed  vegetable 
matter  in  it. 

Humus.  This  decayed  vegetable  matter  in  the  soil 
is  known  as  humus,  or  mold.  An  adequate  supply  of 
humus  is  of  the  greatest  importance  in  agricultural  lands, 
and  whenever  possible  vegetable  matter  should  be  re- 
turned to  the  land.  Not  only  does  the  decaying  humus 
provide  plants  with  certain  food  elements  that  they  need, 
but  it  also  makes  a  soil  lighter  and  looser  and  greatly  in- 
creases its  water-holding  capacity.  In  reality,  the  humus 
in  a  soil  is  as  much  a  part  of  it  as  are  the  rock  particles ; 


174  Science  for  Beginners 

and  it  should  be  added  that  a  complete  definition  of  soil 
includes  also  the  water  and  air  and  the  many  forms  of 
lowly  life  that  abound  in  every  handful  of  earth.1 

The  science  of  agriculture.  You  must  not  think 
that  after  reading  this  brief  discussion  of  soils,  you  are 
completely  informed  concerning  the  adaptation  of  the 
different  kinds  of  soil  to  the  raising  of  crops.  The 
purpose  here  is  only  to  enable  you  to  appreciate  in  a 
general  way  the  somewhat  simple  classifications  of  soils 
that  are  used  and  the  technical  terms  that  are  applicable 
in  each  case.  It  is  to  be  hoped  that  in  the  future  you 
will  be  able  to  study  the  science  of  agriculture,  whether 
you  live  in  the  country  or  the  city ;  for  no  more  interest- 
ing life  is  possible  than  that  of  the  intelligent  farmer  who 
successfully  uses  a  knowledge  of  science  to  bend  the  forces 
of  nature  to  his  will. 

1  Fill  a  flower  pot  with  soft,  dark  earth  and  mold  from  the  border  of 
the  wood,  and  carry  it  to  the  student  of  entomology,  to  see  if  he  can 
name  one  half  of  the  living  forms  of  this  little  kingdom  of  life ;  or  hand  it 
to  the  botanist,  well  trained  in  the  lower  orders  of  plants,  to  see  how 
many  of  the  living  forms  which  these  few  handfuls  of  dirt  contain  he  can 
classify.  Present  this  miniature  farm  to  the  chemist  and  the  physicist, 
and  let  them  puzzle  over  it.  Call  in  the  farmer,  and  ask  him  what 
plants  will  thrive  best  in  it ;  or  keep  the  soil  warm  and  moist  for  a  time 
and  have  the  gardener  say  of  the  tiny  plants  that  appear  as  by  magic, 
which  are  good  and  which  are  bad.  Mark  what  all  these  experts  have 
said,  and  call  in  the  orchardist  to  tell  you  how  to  change  dead,  lifeless, 
despised  earth  into  fruit;  ask  the  physiologist  to  explain  how  sodden 
earth  is  transformed  into  nerve  and  brain.  —  ROBERTS. 


CHAPTER  NINETEEN 

THE  POTATO 

• 
A  FURTHER  STUDY  OF  THE  SOIL 

THE  average  yield  per  acre  of  potatoes  throughout  the 
United  States  is  about  100  bushels,  but  when  potatoes 
are  properly  grown,  yields  of 
250  or  300  bushels  per  acre  are 
frequently  obtained  over  large 
areas.  There  are  many  records 
of  more  than  500  bushels  per 
acre,  and  one  yield  of  more 
than  750  bushels  per  acre  has 
been  reported.  How  can  these 
large  yields  be  secured? 

An  excursion  to  the  garden 
and  a  scientific  study  of  some  of 
the  facts  to  be  observed  there 
will  not  only  help  us  in  some 

FIG.  ioo.    A  potato  plant. 

measure  to  answer  this  ques- 
tion but  will  also  teach  additional  lessons  concerning 
the  soil. 

A  potato  an  enlargement  of  an  underground  stem. 
Potatoes  grow  on  underground  stems ;  they  are  in  fact 
only  enlargements  of  the  stem.  They  are  properly 
called  tubers  and  not  roots.  Pull  up  a  hill  of  young 
potatoes  and  find  what  appear  to  be  two  sets  of  roots. 
Carefully  trace  back  to  the  stem,  which  is  above  the 
ground,  those  that  carry  the  potatoes ;  notice  that  they 
are  really  branches  of  the  stem  and  are  quite  distinct 
from  the  real  roots. 


Science  for  Beginners 


FIG.  101.    Measuring  the  length  of  a  potato. 


Exercise  i .  Let  each 
pupil  bring  one  or  more 
potatoes  from  home. 

Weigh  them,  one  by 
one;  compute  the  av- 
erage weight. 

Exercise  2.  Measure 
the  potatoes  as  to  length 
and  thickness  (Fig.  101) ; 
compute  the  average 
length  and  thickness. 


The  man  who  deals  largely  in  potatoes  will  tell  you 
that  those  ranging  from  2  to  3  inches  in  length  and  weigh- 
ing from  5  to  10  ounces  are  most  salable.  If  smaller 
than  this,  they  do  not  cook  uniformly,  and,  when  baked 
or  boiled  whole,  they  do  not  look  so  appetizing.  There 
is  also  slightly  more  waste  in  paring  small  potatoes. 

Exercise  3.  From  the  potatoes  that  have  been  brought 
to  school,  sort  out  those  that  are  most  salable. 

Selecting  seed  potatoes.  In  selecting  seed  potatoes, 
dig  each  hill  separately  and  keep  for  seed  the  potatoes 
from  the  hill  yielding  the  largest  number  of  the  desirable 
size.  Satisfactory  results  cannot  be  secured  by  selecting 
the  best  potato  from  a  hill ;  for  a  large,  smooth  specimen 
may  be  the  only  good  potato  produced  in  the  hill.  A 
plant  that  has  been  able  to  produce  but  one  good-sized 
potato  is  not  strong  enough  to  bear  good  seed. 

Exercise  4.  Have  all  the  potatoes  brought  in  from  several 
hills,  selecting  low-yielding  as  well  as  high-yielding  hills. 
Then  repeat  Exercises  i  and  2  and  find  out  which  hill  pro- 
duced the  most  potatoes  of  a  desirable  size. 


The  Potato 


177 


From  photograph  by  U .  S.  Department  of  Agriculture 

FIG.  102.    The  yield  from  two  hills  of  potatoes  of  the  same  variety,  grown  in 
the  same  kind  of  soil  and  under  the  same  conditions. 

Would  it  be  better  to  save  seed  from  a  very  large 
watermelon,  pumpkin,  or  tomato  that  was  the  only  one 
produced  on  the  plant,  or  from  a  moderate-sized  one 
grown  on  a  plant  that  had  produced  several  others  just 
as  good? 

A  test  of  quality.  A  potato  should  not  only  be  of  a 
certain  size ;  to  be  of  good  quality  it  must  also  contain 
a  certain  percentage  of  starch. 

Exercise  5.  Clean  a  potato  thoroughly,  dry  it  and  weigh 
it.  Cut  it  into  halves  and  with  a  common  grater  reduce  all 
of  it  to  a  fine  pulp.  Now  fold  the  pulp  in  a  cotton  or  linen 
cloth  and  wash  it  with  considerable  clean  water,  preserving 
all  the  wash  water.  Allow  the  sediment  to  settle  and  then 
draw  off  the  water  and  dry  the  residue.  This  is  pure  potato 
starch.  Weigh  the  dry  starch  and  compute  its  percentage 
of  the  whole  weight  of  the  potato. 

If  the  percentage  of  starch  falls  below  a  certain  stand- 
ard (about  17  per  cent),  the  reason  probably  is  that  the 


178  Science  for  Beginners 

tubers  have  not  developed  properly,  have  not  ripened, 
or  have  grown  under  adverse*  climatic  or  soil  conditions. 
Such  potatoes,  when  prepared  for  food,  will  not  meet  the 
standard  set  for  table  potatoes  in  this  country. 

The  test  for  starch.  The  following  experiment  shows 
the  method  used  by  the  chemist  to  detect  the  presence 
of  starch. 

Exercise  6.  Put  some  of  the  starch  in  boiling  water; 
it  forms  a  paste  but  does  not  dissolve.  Treat  the  paste  with 
a  few  drops  of  iodin  solution  formed  by  dissolving  2  parts 
of  iodin  and  5  parts  of  potassium  iodid  in  100  parts  of  water ; 
the  starch  is  colored  a  dark  blue.  Add  the  iodin  solution 
to  the  surface  of  a  cut  potato.  A  blue  color  is  produced. 

The  potato  is  not  the  only  plant  that  manufactures 
starch.  Test  an  apple,  corn,  and  other  vegetables  for 
starch. 

Cooking  starchy  foods.  Raw  starch  is  not  easily 
digested,  and  hence  potatoes  and  other  vegetables 
and  green  fruits  should  be  thoroughly  cooked.  In  ripe 
fruits  most  of  the  starch  has  been  changed  to  sugar, 
which,  because  it  is  readily  soluble,  is  easily  digested 
without  cooking.  A  mealy  boiled  potato  is,  in  fact, 
near  akin  to  a  lump  of  sugar ;  for  the  potato,  like 
all  forms  of  starchy  food,  must  be  turned  into  a 
kind  of  sugar  before  it  can  be  absorbed  into  the 
system. 

Color  of  the  potato.  Another  important  thing  to 
notice  is  the  color  of  the  potato.  In  northern  latitudes 
potatoes  with  light  yellow  or  whitish  skin  are  preferred, 
while  in  many  of  the  southern  states  the  pink-skinned 


The  Potato 


179 


The  Country  Gentleman 
FIG.  103.    Harvesting  potatoes  in  Maine. 

tubers  are  liked  better.  As  far  as  experts  have  been 
able  to  determine,  the  color  of  the  skin  has  nothing  to  do 
with  the  eating  qualities  of  the  potato. 

The  texture  of  the  skin.  A  third  point  to  consider 
in  judging  potatoes  (what  are  the  two  already  men- 
tioned?) is  whether  the*  tubers  have  a  smooth,  clear 
skin  or  have  one  more  or  less  netted.  Those  of  the 
latter  character  are  usually  preferred ;  for  it  may  be 
noticed  that  those  which  have  a  smooth  or  clear  skin  are 
apt  to  be  excessively  watery  and  soggy  after  cooking, 
while,  on  the  other  hand,  those  with  netted  appearance 
or  corky  touch  have  a  tendency  to  become  mealy  upon 
boiling. 

Deep  eyes  objectionable.  Again,  potatoes  with  nu- 
merous eyes  and  with  deep  eyes  are  objectionable,  because 
the  eyes  carry  much  dirt,  and  the  labor,  time,  and  waste 
in  preparing  them  for  cooking  is  much  greater  than  is 


180  Science  for  Beginners 

the  case  with  potatoes  of  an  even  surface.     The  same 
objections  apply  to  potatoes  of  irregular  shape. 

Testing  quality  with  a  knife.  A  crisp,  snappy  condi- 
tion of  a  potato  when  cut  indicates  an  abundance  of 
starch  grains.  When  the  cut  is  leathery,  soft,  smooth, 
and  even,  it  indicates  an  overgrowth  of  fiber  in  the  potato 
and  an  inadequate  supply  of  starch.  In  the 
first  case  there  is  sufficient  starch  to  swell 
the  tuber  and  make  it  mealy  when  boiled. 
In  the  second  case  there  is  not  enough  starch 
present  to  break  up  the  structure,  and,  in 
cooking,  the  tuber  retains  its  form  and  often- 
times is  watery  and  soggy. 

Conditions  necessary  to  produce  good 
potatoes.  If  now  we  seek  to  know  the  con- 
ditions of  growth  which  will  produce  good 
potatoes,  we  shall  find  that  mealiness,  when 
cooked,  and  also  a  good  flavor,  depend  in  the 
main  upon  three  conditions : 

First,  and  most  important  perhaps,  is  the 
daily  range  of  temperature  of  the  air  and  the 
soil.  Though  it  cannot  be  laid  down  as  an 
absolute  rule,  it  is  believed  that  g9od  quality 
is  developed  under  a  soil  temperature  of  be- 
tween 65  and  75  degrees  F.  Let  us  stop  and 
ascertain  what  this  statement  means. 

Exercise  7.  Hang  a  thermometer  at  some 
point  in  a  potato  field,  i  foot  from  the  ground, 
A^oil  ther-  anc*  ta^e  ^e  temperature  of  the  air.  Place  the 
mometer.  bulb  of  the  thermometer  upon  the  surface  of  the 


The  Potato 


181 


ground  and  note  the  temperature.  Thrust  it  2  inches  into 
the  ground,  then  4  inches,  6  inches,  and  8  inches,  taking  the 
temperature  at  each  depth.  Repeat  these  observations 
several  times,  so  as  to  obtain  the  average  temperature  for 
each  depth. 

Repeat  the  above  observations  several  times  through  the 
season  while  the  crop  is  growing,  recording  the  results  in 
a  table  like  the  following : 

TEMPERATURE   OF  AIR   AND   SOIL  OF   POTATO   FIELD 


DATE 

TIME  OF 
DAY 

TEMPERATURE 
OF  AIR 

TEMPERATURE  OF  Son. 

Surface 

2  in. 

4  in. 

6  in. 

8  in. 

t 

Would  a  sandy  or  a  clay  soil  be  best  for  raising  early 
potatoes?  Why?  In  your  region,  what  kind  of  soil 
do  the  farmers  consider  best  adapted  to  potatoes? 

Exercise  8.  On  a  sunny  day  late  in  spring  take  the  tem- 
perature of  the  soil  on  the  north  side  and  on  the  south  side 
of  a  hill.  Results?  Is  a  northern  or  a  southern  slope  better 
for  early  potatoes? 

A  second  consideration  of  great  importance  in  raising 
potatoes  is  the  depth  at  which  the  seed  should  be  planted. 


182 


Science  for  Beginners 


We  may  study  with  profit  some  results  obtained  at 
the  Agricultural  Experiment  Station  of  Cornell  Uni- 
versity. 

TABLE  SHOWING  THE  EFFECTS  OF  PLANTING  POTATOES  AT  DIFFERENT 

DEPTHS 


8> 

8? 

8c 

Depth  planted 

2" 

f 

6" 

Number  of  tubers  

IOCO 

996 

QI3 

Weight  in  kilos  l 

74.  867 

86  812 

1  1  -1    A  A 

(  Large 

204. 

AT.? 

4.06 

Size  of  tubers  (  0      ,. 
\Small       

(  Number  of  tubers    . 
Exposed  to  sun  <  ,T7  .  ,  ,  .    ,  ., 
\  Weight  in  kilos  .     . 

756 
514 
28.712 

56l 
204 
13.617 

417 
113 
15.891 

1 A  kilo  =  2.2  pounds;  a  bushel  of  potatoes  weighs  60  pounds. 

At  what  depth  of  planting  was  the  greatest  number  of 
potatoes  found?  At  what  depth  was  the  greatest 
weight  produced? 

Considering  the  last  two  questions,  what  can  you  say 
concerning  the  size  of  the  tubers  in  each  case  ? 

What  is  meant  by  the  statement  that  "  the  number 
of  the  potatoes  in  the  hill  varies  inversely  as  the  depth 
of  planting  "  ? 

Is  there  any  good  reason  why  the  size  of  the  potatoes 
should  not  have  been  larger  if  the  seed  tubers  had  been 
planted  8  inches  deep  ?  Ought  we  to  take  the  tempera- 
ture of  the  soil  into  account? 

Exercise  9.  In  each  of  the  three  cases  above  compute 
the  percentage  of  large  and  small  potatoes ;  enter  the  results 
in  a  table  and  state  your  conclusion.  In  each  case  figure 
out  the  percentage  of  exposed  potatoes. 


The  Potato 


183 


The  Country  Gentleman 
FIG.  105.    A  potato  field  in  the  irrigated  region  of  Colorado. 

No  tubers  were  found  growing  deeper  than  the  seed  was 
planted.  This  teaches  us  that  the  time  to  regulate  the 
depth  at  which  the  potatoes  are  to  grow  is  in  planting. 
Of  course,  the  final  depth  can  also  be  regulated  by  the 
amount  of  soil  which  is  placed  over  the  hill.  When 
planted  shallow,  potatoes  are  more  likely  to  become 
exposed  to  the  direct  rays  of  the  sun,  in  which  case 
they  turn  green  and  are  spoiled  for  food. 

In  the  third  place,  the  quality  of  the  potato  and  the 
yield  per  hill  depend  upon  the  degree  of  ripeness  of  the 
tubers  when  the  plant  dies.  Young  tubers  taken 
from  green  and  growing  plants  are  better  than  unripe 
tubers  taken  from  plants  that  are  dead.  The  best 
potatoes  are  those  that  ripen  fully  while  the  top  is  still 
green. 

What  is  the  average  yield  per  acre  of  potatoes  in  your 
locality?  Ask  the  farmers. 


184  Science  for  Beginners 

What  have  been  the  ruling  prices  for  potatoes  in  the 
market  for  the  past  three  or  four  years  ?  Ask  the  farmer 
and  the  grocer. 

The  best  soil  for  the  potato.  The  potato  requires  a 
fertile  soil.  A  rich,  sandy  loam  well  supplied  with  or- 
ganic matter  and  well  drained  is  the  best,  although  pota- 
toes may  be  grown  on  nearly  every  class  of  soil.  Very 
heavy  clay  is  not  good  and  should  not  be  used  if  the 
farm  affords  any  lighter  soil.  Potatoes  are  often  raised 
on  light,  sandy  soils,  but  such  a  soil  must  be  well  fer- 
tilized. 

One  year,  or  at  the  most  two  years,  is  the  longest 
time  potatoes  should  be  grown  on  the  same  field.  This  is 
especially  true  if  there  has  been  a  tendency  to  diseases 
of  any  kind.  A  clean  crop  cannot  be  expected  from  a 
field  which  has  produced  scabby  tubers.  The  germs  that 
cause  the  scab  live  in  the  soil,  but  they  can  be  starved 
out  by  growing  other  crops  on  the  land  for  several  years. 

In  the  central  part  of  the  United  States  and  elsewhere 
a  rotation*  of  crops  has  given  very  satisfactory  results, 
and  large  yields  of  potatoes  have  been  secured.  The 
rotation  may  be :  fall  wheat,  in  which  clover  is  sown  in 
spring ;  second  year,  clover  plowed  under  in  the  fall  or 
winter ;  and  the  third  year,  potatoes. 

The  lesson  to  be  learned.  You  must  not  think  that 
the  object  of  this  chapter  is  merely  to  teach  facts  con- 
cerning the  growth  and  culture  of  the  potato.  It  is 
intended  to  do  this,  it  is  true ;  but  the  primary  object 
of  this  study  is  to  show  how,  by  careful  observation  and 
study  of  facts,  conclusions  may  be  reached  and  out  of 


The  Potato  185 

these  conclusions  there  may  be  developed  a  method  by 
which  the  largest  and  most  profitable  crops  may  be  pro- 
duced from  the  soil.  You  are  to  see  how  your  scientific 
method  may  be  employed  in  this  and  similar  cases  to 
raise  farming  from  mere  drudgery  to  an  intensely  in- 
teresting scientific  pursuit. 


CHAPTER  TWENTY 

A   STUDY   OF  THE   AIR 

NUMEROUS  animals,  as  the  mole  and  the  earthworm, 
spend  their  whole  existence  underground.  Some  of 
them  will  seek  the  surface  occasionally,  in  a  storm  or  in 
the  darkness  of  night ;  but  when  they  do  this,  they  are 
away  from  their  natural  home  and  are  blind  to  the  beau- 
ties and  advantages  of  life  above  ground. 

Other  animals  live  in  the  water  that  covers  the  greater 
part  of  the  earth.  Some  of  them,  as  the  whale  and  the 
porpoise,  come  to  the  surface  of  the  water  only  to 
breathe ;  others,  like  the  minnow,  the  shark,  the  carp, 
and  the  eel,  sometimes  break  the  surface  of  the  water  to 
take  food  that  is  floating  there ;  but  many  animals  know 
no  life  except  one  that  is  lived  far  beneath  the  surface 
of  the  water. 

Plants  occupy  two  different  zones ;  they  lead  a  double 
life.  The  roots  of  the  clover,  the  corn,  the  grape,  the 
pine,  and  the  palm  lead  a  busy  life  beneath  the  soil. 
The  tops  push  up  to  a  freer  existence  in  the  air. 

Man  lives  upon  the  surface  of  the  earth.  He  is  fitted 
to  live  in  the  air.  As  the  deep-sea  animals  live  at  the 
bottom  of  an  ocean  of  water,  so  man  spends  his  existence 
at  the  bottom  of  an  ocean  of  air.  This  air,  or  atmos- 
phere, is  of  the  greatest  interest  to  us  all.  It  is  the 
subject  of  our  study  in  this  chapter. 

The  air  a  material  substance.  First  of  all  we  should 
prove  to  our  satisfaction  that  the  air  is  really  a  mate- 
rial substance.  Review  the  experiments  described  on 
page  29. 

186 


A  Study  of  the  Air 


187 


Exercise  i.  Move  your  hand 
quickly  back  and  forth  and  convince 
yourself  that  there  is  an  invisible 
something  all  about  you.  Use  a  fan 
in  order  to  prove  the  presence  of  the 
air  more  plainly. 

Exercise  2.  Stand  out  of  doors 
in  the  wind  and  consider  what  it  is 
that  meets  you  in  the  face  and  disar- 
ranges your  hair  and  clothing. 

The  chemical  composition  of  air. 

Figure  107  shows  a  bell  jar,  or,  as 
it  is  commonly  called,  a  receiver, 
open  at  the  bottom.  An  old  bot- 
tle with  the  bottom  cracked  off 
may  be  used  instead,  in  the  fol- 
lowing interesting  experiment : 

Exercise  3.  Carefully  dry  a  small 
piece  of  phosphorus  no  larger  than 
a  small  pea  by  pressing  it  between 
folds  of  blotting  paper.1  Place  it 
on  a  cork  floating  on  the  water  in 
a  basin.  Light  the  phosphorus  with 
a  hot  wire  and  quickly  set  the  bell 
jar  over  it. 

Caution!  Take  great  care  in 
handling  phosphorus.  Keep  it  under 

1  The  essential  features  of  this  experi- 
ment may  be  shown  by  lighting  a  piece  of 
paper,  throwing  it  upon  the  surface  of  some 
water,  and  holding  a  tumbler  over  it. 


FIG.   106.    We  live  at  the 
bottom  of  an  ocean  of  air. 


i88 


Science  for  Beginners 


FIG.  107. 


When  the  phosphorus  burns  the  water  rises  in 
the  bell  jar. 


water  when  not 
using  it  and 
never  touch  it 
with  your  fin- 
gers, as  it  may 
adhere  to  the 
skin  and  burn 
you  severely. 

What  chem- 
ical action  is 
going  on  while 
the  phosphorus 
burns  ?  Why 
does  it  cease  to 
burn?  What 
is  the  chem- 
ical name  of 
the  white  com- 
pound which 


composes  the  fumes  (page  95)  ?  its  chemical  composition  ? 

Let  the  jar  stand  for  some  time.  The  white  fumes  will 
dissolve  as  they  fall  into  the  water.  Notice  that  at  the  same 
time  the  water  has  risen  about  one  fifth  of  the  way  up  the  jar. 
This  fact  will  lead  to  an  important  conclusion  a  little  later. 

Is  the  gas  which  remains  in  the  receiver  the  same  as 
the  air  which  we  first  inclosed  in  the  bell  jar  ?  This  is  a 
question  that  should  be  answered  with  great  care.  The 
next  exercise  will  give  you  the  answer. 

Exercise  4.  Light  a  pine  stick.  Will  it  continue  to  burn 
as  long  as  you  leave  it  in  the  open  air?  Take  the  stopper 
from  the  bell  jar  and  plunge  the  lighted  stick  into  the  gas 
in  the  jar.  The  flame  suddenly  goes  out.  Repeat  the  experi- 


A  Study  of  the  Air  189 

ment.     Try  the  same  experiment  in  a  bottle  or  receiver 
containing  ordinary  air. 

We  have  here  come  face  to  face  with  some  facts  con- 
cerning the  chemical  constituents  of  the  air : 

(1)  There  is  something  in  the  air  which  has  united 
with  the  phosphorus  and  burned  it.     In  that  chemical 
action  both   the  phosphorus   and   the   something   dis- 
appeared and  water  rose  in  the  jar  and  took  its  place. 

(2)  There  was  something  in  the  air  which  did  not  unite 
with  the  phosphorus  and  that  something  remained  in  the 
jar.     How  do  you  know  there  was  something  in  the  jar 
after  the  phosphorus  was  burned?     We  conclude  that 
the  air  is  made  up  of  at  least  two  substances. 

Nitrogen  and  oxygen  in  the  air.  The  gas  that  re- 
mained in  the  jar  is  nitrogen.  It  is  one  of  the  two  princi- 
pal gases  which  go  to  make  up  the  air.  About  what 
proportion,  by  volume,  of  the  atmosphere  is  nitrogen? 
Something  that  happened  in  Exercise  3  should  enable  you 
to  answer  this  question.  Nitrogen  is  a  non-supporter 
of  combustion,  as  you  proved  in  the  last  experiment. 

The  gas  which  has  been  removed  from  the  air  in  the 
jar  is  oxygen.  As  we  learned  in  Chapter  Six,  oxygen 
aids  or  supports  combustion,  or  burning.  Review  the 
experiment  with  the  iron  picture  cord  and  oxygen  as 
given  on  page  48.  Is  not  the  advantage  of  having  the 
air  composed  in  part  of  nitrogen  very  evident?  If  the 
air  consisted  entirely  of  oxygen,  all  things  would  burn 
very  much  more  rapidly  than  they  now  do.  In  fact, 
not  only  would  the  coal  or  wood  burn  in  the  stove,  but 
the  stove  itself  would  burn, 


Science  for  Beginners 

Both  oxygen  and  nitrogen  are  transparent,  colorless, 
tasteless,  and  odorless  gases.  How  do  you  know  this? 
Are  your  nose  and  mouth  full  of  air  at  this  moment? 

The  proportions  of  oxygen  and  nitrogen  in  the  air. 
The  exact  proportions  of  oxygen  and  nitrogen  in  air 
that  has  been  freed  from  water  vapor,  carbon  dioxid, 
and  other  substances  is : 

BY  VOLUME  BY  WEIGHT 

Oxygen  20.9%  23.1% 

Nitrogen  (including  argon)         79.1  y6.Q 

100%  100% 

Nitrogen  an  inactive  element.  Nitrogen  is,  in  its 
chemical  nature,  extremely  inactive ;  that  is,  it  does  not 
readily  unite  with  other  elements.  For  example,  it  has 
been  mixed  with  the  oxygen  in  the  air  during  all  the 
thousands  of  years  that  have  passed  since  the  atmosphere 
of  the  earth  was  formed ;  and  yet,  in  spite  of  the  intense 
activity  of  oxygen,  the  nitrogen  and  oxygen  are  only 
mixed  in  the  atmosphere,  —  they  are  not  chemically 
combined.  A  lightning  stroke  will  compel  them  to 
unite,  forming  a  very  small  amount  of  nitric  acid  (HNOs) ; 
but  in  the  air  it  is  only  in  this  very  unusual  way  that  the 
union  is  brought  about. 

Nitrogen  compounds  not  plentiful.  In  view  of  the 
facts  stated  in  the  last  paragraph,  we  are  prepared  to 
learn  that  compounds  of  nitrogen  are  not  very  plentiful. 
They  are  found  in  any  considerable  amount  in  only  a 
few  places,  and  these  places  are,  for  the  most  part,  not 
in  the  United  States.  Near  the  boundary  between  Chile 
and  Peru  are  found  great  beds  of  Chile  saltpeter,  or 


A  Study  of  the  Air 


191 


From  photographs  furnished  by  Pan- A  merican  Union 
FIGS.  108  and  log.    Views  in  the  sodium  nitrate  fields  of  Chile. 

sodium  nitrate  (NaNOs),  and  for  years  past  many  of 
the  nations  of  the  earth  have  been  going  to  that  region 
for  their  nitrogen  supply. 

Our  lives  dependent  upon  compounds  of  nitrogen. 
Every  living  plant  and  animal  is  built  partly  of  nitrogen, 
and  the  continuance  of  the  life  of  all  living  things  depends 
on  their  being  able  to  procure  compounds  of  nitrogen 
for  food.  Over  every  acre  of  ground  there  are  thousands 
of  tons  of  nitrogen,  but  animals  and  ordinary  plants 
cannot  use  it  in  this  free,  or  uncombined,  form.  The 
nerves,  muscles,  and  glands  of  our  bodies  are  compounds 
of  nitrogen,  and  we  must  have  compounds  of  nitrogen 
in  our  food.  Plants  likewise  must  have  nitrogen  com- 
pounds which  they  get  from  the  soil.  In  ordinary  soil 
only  a  small  supply  of  nitrogen  compounds  is  present, 
and  one  of  the  great  problems  in  agriculture  is  to  keep 
sufficient  nitrogen  in  the  land. 

Help  from  the  legumes.  What  shall  be  used  for  fuel 
when  the  beds  of  coal  are  all  gone  is  an  important  ques- 


Science  for  Beginners 


tion.  It  is  likewise  a  question  of  vital  importance  how 
the  people  of  the  world  can  be  supplied  with  nitrogen 
compounds  when  the  South  American  deposits  that  we 
are  now  using  shall  have  been  exhausted.  In  our  diffi- 
culties we  often  get  relief  from  unexpected  quarters, 
and  in  this  case  it  seems  that  we  shall  be  saved  from  a 
nitrogen  famine  by  the  legumes,*  a  certain  family  of 
plants.  This  family  includes  the  clovers,  alfalfa,  peas, 
beans,  and  the  vetches.  Unlike  other  plants,  these 
plants  do  not  use  what  nitrogen  they  find  in  the  soil  and 
then  leave  the  soil  much  poorer  in  that  material ;  they 
have  means  by  which  they  draw  nitrogen  from  the  air 
and  make  compounds  of  it  for  their  use. 

Exercise  5.  Pull  up  a  clover  or  alfalfa  plant  and  notice 
on  its  roots  numerous  small  swell- 
ings, called  tubercles.  If  you  were 
to  crush  one  of  these  tubercles  and 
examine  it  with  a  powerful  mi- 
croscope, you  would  find  thou- 
sands of  tiny,  living  bacteria* 
growing  in  it. 

The  secret  of  the  clover  plant. 
The  bacteria  in  the  tubercles 
take  nitrogen  from  the  air  and 
combine  it  with  other  elements 
that  will  make  food  for  the 
plants.  Notice  that  it  is  not  the 
clover  plant  itself  that  possesses 
this  power.  This  very  important  work,  so  necessary  to  all 
mankind,  is  done  by  these  smallest  of  living  plants,  the 


FIG.  no.  Tubercles  on  the  roots 
of  a  clover  plant. 


A  Study  of  the  Air 


193 


FIGS,  in  and  112.    When  the  leaves  are  burned  the  nitrogen  escapes  into  the 
air.    But  when  they  are  buried  the  nitrogen  in  them  is  returned  to  the  soil. 

bacteria.  The  clover  gives  them  a  place  to  live  in  and  do 
their  work.  Then  it  absorbs  the  compounds  produced  by 
the  bacteria  into  its  roots  and  uses  them  in  its  growth. 

So  you  can  now  understand  how  it  is  that  the  clover 
plant  not  only  provides  its  own  nitrogenous  food,  but, 
if  it  is  plowed  into  the  soil  or  if  its  roots  decay  in  the 
ground,  leaves  in  the  soil  a  large  amount  of  such  food 
for  other  plants.  The  leguminous*  plants  also  contain 
the  nitrogen  compounds  that  are  necessary  to  animals, 
and  they  are  eaten  by  the  ox  and  other  herbivorous* 
animals.  These  in  turn  are  used  as  food  by  man,  so  you 
must  thank  the  clover  plant  or  some  of  its  relatives  and 
the  little  bacteria  that  are  partners  in  the  work,  both  for 
the  meat  that  you  eat  and  the  bread  that  the  nitrogen 
enables  the  wheat  plant  to  furnish  you. 

"  Sweetening  "  acid  soil.  Bacteria  that  have  the  power 
to  fix  or  combine  nitrogen  cannot  live  in  an  acid  soil, 


194  Science  for  Beginners 

and  clover  and  alfalfa  will  not  flourish  in  such  soil  until 
the  acid  has  been  neutralized.  Slaked  lime  and  finely 
ground  limestone  are  much  used  for  this  purpose.  Lime- 
stone can  often  be  found  in  the  form  of  finely  divided 
marl  in  the  bottoms  and  along  the  shores  of  freshwater 
lakes,  and  this  marl  may  be  used  to  sweeten  acid  soil. 

Keeping  up  a  supply  of  soil  nitrogen.  It  should  be 
remembered  that  all  decaying  vegetables,  plants,  leaves, 
and  barnyard  manure  contain  compounds  of  nitrogen. 
They  should  be  returned  to  the  soil  so  that  other 
plants  can  make  use  of  the  nitrogen.  It  is  wrong  for 
the  gardener  to  burn  the  leaves  that  fall  from  the  trees, 
for  when  this  is  done  the  nitrogen  returns  to  the  air  in 
the  free  state.  For  the  same  reason  the  farmer  should 
return  to  the  soil  every  form  of  decaying  vegetable  life, 
—  the  manure  from  the  barnyard,  straw,  cornstalks, 
and  green  plants. 

Commercial  fertilizers.  Combined  nitrogen  can  be 
bought  in  the  form  of  ammonium  sulfate  [(NH4)2S04], 
sodium  nitrate  (NaNO3),  or  potassium  nitrate  (KN03). 
These  are  mixed  with  the  other  elements  which  also  are 
necessary  to  the  growth  of  plants  and  are  sold  as  com- 
mercial fertilizers.  The  two  elements  besides  nitrogen 
that  are  often  lacking  in  soils  are  potassium  and 
phosphorus  (page  97). 

A  study  of  ammonia.  One  of  the  most  common  com- 
pounds of  nitrogen  is  ammonia  (NHs).  A  brief  study  of 
this  compound  may  be  made  as  follows : 

Exercise  6.  Procure  a  small  amount  of  ammonium 
chlorid,  or  sal  ammoniac.  Examine  it  carefully.  It  is  a 


A  Study  of  the  Air 


195 


FIG.  113. 


Preparing   and    collecting   am- 
monia. 


white  crystalline  solid, 
has  a  sharp,  caustic 
taste,  and  yields  no  odor. 
Place  a  small  amount 
of  powdered  quicklime  in 
the  palm  of  one  hand 
and  a  like  amount  of 
ammonium  chlorid  in  the 
palm  of  the  other  hand. 
Then  rub  the  two  to- 
gether. Very  quickly  a 
strong  odor  of  ammonia 
is  developed.  Hold  a 
moist  piece  of  red  litmus 
paper  in  the  gas  which  is 
coming  from  your  hands. 

Ammonia  is  a  colorless,  irrespirable*  gas,  has  a  strong 
odor,  and  is  lighter  than  air.  The  ammonia  that  is  sold 
for  household  use  is  made  by  dissolving  the  gas  in  water. 
As  you  have  learned  from  your  experiments,  ammonia  is 
an  alkali,  and  acids  may  be  neutralized  by  it  (page  90). 
In  its  gaseous  form  ammonia  is  used  to  produce  the 
cold  in  ice  factories  and  in  cold  storage  plants  (page  2,59). 

A  striking  experiment.  Ammonia  is  soluble  in  water 
to  such  an  extent  that  1000  cubic  feet  of  the  gas  can 
be  dissolved  in  i  cubic  foot  of  water.  This  fact  can  be 
made  the  basis  of  a  most  interesting  experiment. 

Exercise  7.  Heat  in  a  flask  a  mixture  of  quicklime  and 
ammonium  chlorid  and  collect  the  ammonia  that  is  given  off 
by  downward  displacement  of  air  (Fig.  1 13).  Close  the  bottle 
with  a  stopper  through  which  is  passed  a  glass  tube,  and 


Science  for  Beginners 


then  arrange  in  the  manner 
shown  in  Figure  114  a 
vessel  of  water  colored  red 
with  litmus.  The  liquid 
rushes  up  into  the  bottle 
and  turns  blue.  Explain  (i) 
why  the  litmus  water  enters 
the  bottle  and  (2)  why  it 
changes  its  color.  Perhaps 
you  will  be  able  to  answer 
the  first  of  these  questions 
better  after  your  study  of 
the  next  chapter. 

Use  of  nitrogen  com- 
FlG-  II4-  pounds  in  war.     Potas- 

sium nitrate  is  used  to  make  gunpowder  and  other  forms 
of  explosives.  Guncotton  is  made  by  treating  cotton 
with  nitric  acid,  and  dynamite  also  is  a  nitrogen  com- 
pound. Nitrogen  compounds  are  used  in  immense 
quantities  in  times  of  war.  By  using  electricity  it  is 
possible  to  make  nitric  acid  from  the  nitrogen  in  the 
air,  and  from  nitric  acid  almost  any  desired  nitrogen 
compound  can  be  made.  The  United  States  government 
is  now  spending  many  millions  of  dollars  on  a  great 
nitrate  plant  so  that  we  may  have  a  supply  of  nitrogen 
compounds  produced  within  our  own  borders.  Every 
time  a  great  gun  is  fired  a  large  amount  of  nitrogen  is 
set  free  and  is  no  longer  of  any  use  to  man. 

Other  gases  in  the  air.  In  a  former  chapter  we 
learned  that  there  is  carbon  dioxid  in  the  atmosphere 
(page  109).  This  is  present  in  very  small  amounts; 


A  Study  of  the  Air 


197 


there  are  only  about  4 
parts  of  carbon  dioxid  in 
10,000  parts  of  air.  A 
small  quantity  of  am- 
monia formed  by  the 
decomposition  of  animal 
and  vegetable  matter 
also  exists  in  the  air,  and 
there  is  a  considerably 
larger  amount  of  argon,  a 
gas  which  can  be  detected 


FIG.  115.    Why  does  the  water  collect 
on  the  outside  of  the  pitcher? 


only  by  the  refined  methods  of  the  chemical  laboratory. 
Water  vapor  is  always  present  in  the  air,  as  you  can 
prove  by  the  following  experiment : 

Exercise  8.  Lay  a  small  piece  of  dry  potash  (KOH)  in 
an  open  dish  and  expose  it  to  the  air.  Water  will  be  taken 
up  from  the  air  and  the  potash  will  be  dissolved.  This  is  a 
proof  of  the  presence  of  water  vapor  in  the  air. 

Another  proof  that  the  air  contains  water  vapor  is 
found  in  the  fact  that  drops  of  water  may  often  be  seen 
upon  the  outside  of  a  pitcher  containing  ice  water. 
These  drops  of  water  do  not  soak  through  the  pitcher 
from  the  inside.  Where  do  they  come  from  (page  63)  ? 
Observe  that  more  water  gathers  on  the  pitcher  on  a 
warm,  humid  day  than  on  a  clear,  cold  day.  Why? 

What  is  the  source  of  dew?    What  is  frost? 


CHAPTER  TWENTY-ONE 

THE  WEATHER 
A  FURTHER  STUDY  OF  AIR 


To  the  minds  of  many  persons 
the  weather  is  something  that 
knows  no  law.  Reckless  and 
lawless,  fickle  and  changeful,  it 
does  as  it  pleases,  —  now  pro-  FIG  Ii6 

viding  a  beautiful  day  for  an 

outing,  a  football  game,  a  picnic;  now  turning  with 
vengeance  against  man  and  nature,  and  uprooting 
forests  and  destroying  life  with  none  to  hinder. 

There  is  some  reason  for  this  conception  of  the  weather ; 
but  we  should  learn  that  nature,  in  all  its  moods,  acts 
under  laws  that  are  uniform  and  unchanging ;  that  there 
is  a  science  of  the  weather  that  is  well  known  to  those 
who  make  a  study  of  the  subject.  Through  the  very 
efficient  labors  of  the  United  States  Weather  Bureau, 
maps  and  bulletins  showing  weather  conditions  in  all 
parts  of  the  country  are  sent  out  daily. 

198 


The  Weather 


199 


FIG.  117.    An  air  globe. 


What  is  the  weather? 
By  the  "weather"  are 
meant  the  temperature, 
moisture,  pressure,  rate 
of  movement,  and  other 
conditions  of  the  atmos- 
phere. It  has  to  do  with 
the  degree  of  heat  or  cold ; 
wetness  or  dryness;  rain 
or  snow ;  calm  or  storm ; 
clearness  of  the  sky  or 
cloudiness;  gentle  breeze 

or    tornado ;     spring    shower    or    blizzard ;     flood    or 
drought. 

This  is  an  important  subject,  having  to  do  with  our 
personal  comfort,  our  health,  and  our  success  or  failure 
in  raising  crops  and  in  transporting  these  products  to 
the  markets  of  the  world.  Indeed,  the  weather  has  its 
influence  upon  every  movement  and  every  activity  of 
human  society,  and  we  should  know  the  common  facts 
about  winds  and  the  causes  of  changes  in  the  weather. 
The  best  way  to  begin  our  study  of  the  subject  is  to 
learn  some  additional  facts  about  air. 

The  weight  of  air.  One  definition  of  matter  is  that 
it  is  anything  that  has  weight.  Is  air  matter?  Can 
you  weigh  it  ?  If  the  school  has  the  apparatus,  you  can 
answer  this  question  by  an  experiment. 

Exercise  i.  Open  the  stopcock  of  an  air  globe  like  that 
shown  in  Figure  117  and  weigh  the  globe.  Attach  an  air 
pump  to  the  globe  and  force  as  much  air  as  possible  into 


200 


Science  for  Beginners 


it.    Now  close  the  stopcock  and  weigh  the  globe.    It  will 
be  found  that  it  has  gained  in  weight.     Why  ? 

From  this  experiment  we  may  conclude  that  air  is 
matter  and  that  it  has  weight.  A  cubic  yard  of  air 
under  ordinary  conditions  weighs  about  2  pounds.  What 
would  be  the  weight  of  the  air  in  a  hall  30  feet  square 
and  12  feet  high? 

Air  and  pressure.  Another  fact  that  we  need  to 
understand  is  that  air  exerts  pressure  on  us  and  on 
everything  about  us. 

Exercise  2.  Bind  a  piece  of  thin  sheet-rubber  over  the 
mouth  of  a  common  clay  pipe ;  put  the  stem  of  the  pipe  in 
your  mouth  and  draw  out  the  air  from  the  bowl.  What 
happens  and  why?  Why  is  not  the  rubber  pressed  down 
when  the  pipe  is  full  of  air? 

Exercise  3.  Fill  a  tumbler  full  of  water,  cover  it  with  a 
sheet  of  writing  paper,  and  invert,  holding  it  at  first  with 
the  hand  without  letting  water  escape  or  any  air  get  inside 
the  paper.  The  air  exerts  a  pressure  from  below  on  the 
paper  more  than  sufficient  to  support  the  weight  of  the 

water.  With  care  the  tumbler 
may  be  held  in  different  posi- 
tions, thus  proving  that  the 
air  presses  alike  in  all  direc- 
tions. 

We  live  at  the  bottom 
of  an  ocean  of  air,  and  just 
as  there  is  great  pressure 
from  the  weight  of  the 
water  at  the  bottom  of  the 
sea,  so  is  there  pressure  at 


FIG.  1 1 8.   The  upward  pressure  of  the 
air  supports  the  water  in  the  glass. 


The  Weather 


201 


the  surface  of  the  earth  from  the  weight  of  the  air  above. 
This  pressure  at  sea  level  is  about  1  5  pounds  to  the  square 
inch.  Like  the  pressure  in 
water,  air  pressure  is  exerted 
in  all  directions,  —  upward, 
downward,  and  laterally.* 

How  much  is  the  pressure 
of  the  air  on  a  square  foot? 
on  a  square  yard?  Why 
does  not  the  pressure  of  the 
air  crush  us  ? 

Exercise  4.  Fasten  a  string 
to  the  center  of  a  round  piece 
of  leather.  Wet  the  leather  to 
make  it  pliable,  and  press  it 
down  evenly  on  a  smooth,  flat 
stone,  making  sure  that  there 
is  no  air  between  the  leather 
and  the  stone.  The  stone,  if 
not  too  heavy,  can  be  lifted  by 
the  string  ;  the  pressure  of  the  air  holds  the  leather  to  the 
stone.  Measure  the  area  of  the  leather  and  compute  the  air 
pressure  upon  it  at  the  rate  of  15  pounds  to  the  square  inch. 
How  does  that  pressure  compare  with  the  weight  of  the 
stone  ?  An  ordinary  plate  may  be  used  for  the  experiment, 
instead  of  the  stone. 

If  the  school  possesses  an  air  pump  and  a  pair  of 
Magdeburg  hemispheres,  an  experiment  can  be  made 
that  shows  in  a  very  striking  way  the  pressure  of  the  air. 
This  experiment  was  first  done  300  years  ago  by  Otto 
von  Guericke,  a  scientist  and  the  burgomaster  of  Magde- 


"£•   The  pressure  of  the  air 

holds  the  sucker  against  the  stone. 


2O2 


Science  for  Beginners 


burg.  The  apparatus  needed 
consists  of  two  brass  hemi- 
spheres (Fig.  120)  which  fit 
each  other  so  as  to  be  perfectly 
air  tight.  When  the  air  is 
drawn  out,  removing  the  inside 
pressure,  a  very  great  force  is 
required  to  pull  them  apart. 

The  hemispheres  used  by 
Guericke  are  in  the  museum  at 
Berlin,  and  with  them  is  a 
Latin  book  which  contains  an 


sphere  and  is  not  shown  in  the 
illustration. 


FIG.  1 20.  The  Magdeburg 
hemispheres  used  by  Otto  von 
Guericke  in  his  famous  experi- 
ment. The  opening  through 
which  the  air  was  exhausted  is  ,.  ,  . 

in  the  bottom  of  the  lower  hemi-     account  of  his  experiment.   His 

hemispheres  had  a  diameter  of 
about  twenty  inches,  and  after 
the  air  was  thoroughly  exhausted  he  hitched  horses  to 
each  hemisphere  in  a  great  tug  of  war.  He  put  eight 
horses  on  a  side  before  the  spheres  could  be  pulled  apart. 
How  many  horses  would  he  have  required  if  he  had 
hitched  one  of  the  hemispheres  to  a  tree? 

Measuring  the  pressure  of  the  air.  The  pressure 
of  the  air  is  measured  by  an  instrument  called  the 
barometer.  The  principle  involved  in  its  use  may  be 
understood  from  the  following  experiment : 

Exercise '5.  Completely  fill  with  mercury  a  glass  tube 
about  32  inches  long,  closed  at  one  end  and  open  at  the  other. 
Place  your  thumb  over  the  open  end.  Then  invert  the  tube 
and  place  the  open  end  in  a  dish  of  mercury.  Immediately 
the  mercury  falls  to  about  30  inches,  measured  from  the  sur- 
face of  the  mercury  in  the  dish. 


The  Weather 


203 


What  holds  the  mer- 
cury up  in  the  tube? 
It  is  the  pressure  of 
the  air  on  the  surface 
of  the  mercury  in  the 
dish.  Is  it  not  clear, 
then,  that  the  height 
of  the  mercury  in  the 
tube  will  change  as  the 
weight  of  the  atmos- 
phere outside  changes  ? 
The  more  heavily  the 
atmosphere  presses  on 
the  surface  of  the  mer- 
cury in  the  dish,  the 
higher  it  will  force  the 
column  of  mercury  in 
the  tube ;  and  if  the  air 
becomes  lighter  and 
presses  with  less  force  on  the  mercury  in  the  dish,  the 
mercury  in  the  tube  will  fall.  Therefore  we  may  expect 
the  barometer  to  show  any  changes  in  air  pressure  as 
they  occur. 

If  you  should  carry  a  barometer  to  the  top  of  a  high 
mountain,  would  the  mercury  in  the  tube  rise  or  fall  ?  Why  ? 

Exercise  6.  Set  up  in  the  schoolroom  the  barometer  which 
you  made  in  the  last  exercise.  Does  the  column  of  mercury 
rise  and  fall  from  day  to  day  ?  Why  ? 

A  barometer  is  an  instrument  for  measuring  the  pres- 
sure  of  the  atmosphere.  The  law  of  the  barometer  is : 


FIG.  121.     Setting  up  a  barometer. 


2O4  Science  for  Beginners 

the  heavier  the  air,  the  higher  the  column  of  mercury ; 
the  lighter  the  air,  the  lower  the  mercury. 

Storms.  The  word  "  storm  "  is  a  very  general  term 
used  to  indicate  a  more  or  less  violent  disturbance  of 
the  atmosphere,  which  is  characterized  by  high  winds  and 
is  accompanied  usually,  but  not  necessarily,  by  some 
form  of  precipitation,  as  rain,  snow,  hail,  or  sleet. 
Storms  are  often  attended  by  electrical  phenomena* 
and  are  then  classed  as  thunderstorms.  Storms  are 
sometimes  named  with  reference  to  some  phenomenon 
that  attends  them ;  thus  we  have  rainstorms,  hailstorms, 
snowstorms,  sandstorms,  cyclonic*  storms,  so  called 
after  the  whirling  motion  of  the  wind.  There  is  also  a 
very  destructive  whirling  local  storm  known  as  a  tornadic 
storm,  or  simply  a  tornado.*  Tornadoes  are  not  of 
wide  distribution  and  occur  only  infrequently.  In  our 
country  they  are  most  common  in  the  Mississippi  Valley 
states  during  the  spring  months. 

Force  exerted  by  winds.  Ordinarily  the  air  is  soft 
and  offers  little  resistance  to  our  passage  through  it. 
We  hardly  feel  it  when  we  are  walking ;  but  if  we  run 
we  notice  it,  and  if  we  go  rapidly  against  it,  as  on  a  bicycle 
or  in  an  automobile,  we  find  its  pressure  quite  strong. 
Whenever  a  storm  arises  and  the  air  moves  with  great 
velocity,  it  exerts  a  tremendous  force.  Speaking  in 
terms  of  the  molecules  of  the  air,  what  is  happening  to 
you  when  the  wind  blows  against  you? 

Exercise  7.  Watch  a  windmill  and  estimate  in  a  general 
way  the  power  and  force  of  the  wind  when  it  is  in  motion. 
Find  out,  by  inquiry,  or  from  books,  how  much  water  a  wind- 


The  Weather 


205 


mill  will  pump  and  what  horse  power  it  develops  in  a 
moderate  wind.  The  Encyclopaedia  Britannica  will  give  you 
information  on  this  subject. 

Force  and  name  of  winds.  The  wind  scale  given  below 
is  in  general  use  throughout  the  world  to  indicate  the 
force  of  the  wind  when  instrumental  measures  are  not 
available.  This  scale  was  proposed  by  the  late  Admiral 
Beaufort,  of  the  United  States  Navy,  and  is  popularly 
known  as  Beaufort's  Scale. 


BEAUFORT'S  SCALE,  USED  IN  PREPARATION  or  ALL  WEATHER  BUREAU 
WIND  FORECASTS  AND  STORM  WARNINGS 


FORCE 

DESIGNATION 

MILES  PER  HOUR 

0 

Calm 

From  o  to  3 

I 

Light  air 

Over  3    to  8 

2 

Light  breeze  (or  wind) 

Over  8    to  13 

3 

Gentle  breeze  (or  wind) 

Over  13  to  18 

4 

Moderate  breeze  (or  wind) 

Over  1  8  to  23 

5 

Fresh  breeze  (or  wind) 

Over  23  to  28 

6 

Strong  breeze  (or  wind) 

Over  28  to  34 

7 

Moderate  gale 

Over  34  to  40 

•      8 

Fresh  gale 

Over  40  to  48 

9 

Strong  gale 

Over  48  to  56 

10 

Whole  gale 

Over  56  to  65 

ii 

Storm 

Over  65  to  75 

12 

Hurricane 

Over  75 

About  how  many  miles  an  hour  will  a  man  or  a  horse 
walk?  How  fast  will  a  freight  train  move?  a  fast 
express  train?  a  steamship?  an  aeroplane?  a  bird? 

A  storm  on  a  small  scale.  It  will  be  an  easy  task  to 
produce  in  the  schoolroom  a  model  of  a  cyclonic  storm  in 


206 


Science  for  Beginners 


FIG.  122.    A  rain  gauge. 


which  we  may  observe 
some  of  the  essential 
features  of  the  great 
storms  that  sweep  over 
the  earth.  A  stub  of 
candle  an  inch  or  so 
high,  a  lamp  chimney, 
and  a  bit  of  smoke 
paper  will  furnish  the 
required  apparatus. 

Exercise  8.  Light  the 
candle  and  with  a  drop 
of  the  melted  wax  an- 
chor it  to  the  table. 
Place  the  chimney  over 
the  flame  and  raise  it  a 
short  distance  above  the 
table  by  placing  small 
pieces  of  a  match  under 
it.  Hold  the  smoking 
paper  in  the  air  above 
the  chimney  and  observe 
the  ascending  column  of 
air.  How  high  does  the 
air  rise?  Be  careful  not 


to  produce  any  air  currents  by  your  own  movements.  Let 
the  candle  do  it  all.  What  finally  becomes  of  the  air  that 
rises? 

Observe  the  currents  of  air  entering  at  the  bottom  of 
the  chimney.  Do  they  come  from  one  direction  or  all 
directions?  Move  away  from  the  chimney  and  see  how  far 


The  Weather 


207 


away  you  can  detect  the  air  currents  setting  in  towards  the 
heated  column. 

The  "  storm,"  as  we  have  produced  it,  thus  far  con- 
sists of :  (i)  a  column  of  heated  air  rising  upward  over 
the  heated  area,  with  (2)  currents  of  air  passing  into 
this  heated  area  from  all  directions. 

Exercise  9.  Carefully  remove  the  lamp  chimney  and  test 
with  the  smoke  paper  as  before.  The  heated  area  will  tend 
to  spread  out  and  the  storm  will  cover  a  larger  area.  Some 
of  our  storms  cover  an  area  several  hundred  miles  or  even  a 
thousand  miles  in  diameter. 


Why  does  the  heated  air  rise  from  the 


Why  air  rises, 
candle? 

Exercise  10.  Set  a  glass  bulb  with  a  long  stem  in  a  vessel 
of  water.  A  bottle  with  a  stopper  arranged  as  shown  in 
Figure  1 24  may  be  used.  Lay 
the  hand  on  the  bulb  or  heat 
it  with  a  lamp.  What 
emerges*  from  the  mouth  of 
the. tube?  Is  there  now  as 
much  air  in  the  bulb  as  there 
was  when  the  air  was  cold? 
Has  the  air  in  the  bulb  lost  in 
weight  ? 

When  air  is  heated  it  ex- 
pands, and  a  cubic  foot  or 
a  cubic  yard  of  such  air  is 
lighter  than  a  cubic  foot  or 
a  cubic  yard  of  cold  air.  It 
therefore  rises,  and  the  cold, 


FIG.  123.    When  the  bulb  is  heated 
the  air  within  it  expand?, 


208 


Science  for  Beginners 


heavier  air  flows  in  from  the 
sides  to  take  its  place.  When 
the  sun  shines  hot  on  an  area 
of  land,  —  as  it  does,  for  example, 
on  India  or  the  southwestern 
part  of  the  United  States  during 
the  summer  months,  —  the  air 
over  such  a  region  expands  and 
becomes  lighter.  This  causes  it 
to  rise,  and  the  winds  move  in 
toward  the  heated  area  from  all 
directions.  An  area  of  light  and 
rising  air  of  this  kind  is  a  storm 
center. 

Cyclones    or    cyclonic    storms. 
There    is  a  very  important  fact 
FIG.  124.  about  cyclonic  storms   that  can- 

not be  shown  in  the  experiment 
with  the  candle.  Because  of  the  rotation  of  the  earth  on 
its  axis,  a  force  arises  which  tends  to  deflect*  to  the  right 
all  motions  in  the  northern  hemisphere.  Consequently 
the  winds  flowing  toward  the  storm  center  are  deflected, 
or  turned,  to  the  right  and  thus  move  spirally  around 
the  storm  center,  as  shown  in  Figure  125.  The  term 
"  cyclone  "  has  been  applied  to  this  system  of  whirling 
winds  around  a  central  region  of  low  pressure,  and 
almost  all  storms  have  this  peculiar  cyclonic  move- 
ment. In  the  tropics  these  motions  are  often  so 
intense  that  they  carry  destruction  and  devastation 
in  their  path;  but  in  the  majority  of  cases  in  extra- 


The  Weather  209 


FIG.  125.    Diagram  to  show  general  directions  of  winds  near  the  surface  of 
the  earth  in  a  cyclone  and  anticyclone  in  the  northern  hemisphere. 

tropical  latitudes  they  are  not  severe.  Note  that  in 
the  center  of  a  cyclone  there  is  a  region  of  low  baro- 
metric pressure. 

Anticyclones.  In  general,  for  every  extra-tropical 
cyclone  there  is  a  corresponding  anticyclone.  The  air 
which  rises  over  a  storm  center  cannot  get  very  far 
above  the  earth  because  it  is  being  pulled  back  to  the 
earth  by  the  force  of  gravity.  This  may  occur  many 
miles  away  from  the  storm  center ;  and  because  the  air 
is  piled  up  in  certain  regions  the  barometric  pressure 
is  increased.  In  other  words,  the  anticyclone  is  an  area 
of  high  barometer,  and  the  circulation  in  an  anticyclone 
is  directly  opposite  to  that  in  a  cyclone.  In  a  cyclone 
the  lower  air  moves  spirally  toward  the  storm  center, 
rises,  and  flows  off  laterally  at  the  top  of  the  column  of 
ascending  air.  In  the  anticyclone  the  upper  air  moves 
toward  the  center,  descends,  and  flows  off  spirally  along 
the  surface  of  the  earth.  In  winter,  areas  of  high  pressure 
often  form  over  the  mountains  of  western  Canada,  and 
from  there  the  cold,  heavy  air  slides  down  as  blizzards 


Science  for  Beginners 

across  the  Dakotas  and  other  states  lying  to  the  east  and 
south. 

On  the  weather  map  the  storm  center  is  indicated  by 
the  word  "  low  "  and  the  anticyclone,  or  area  of  clear 
weather,  is  marked  "  high." 

The  movement  of  storms.  Another  fact  about  cy- 
clonic storms  should  be  noted.  The  storm  as  a  whole 
has  a  progressive  motion  which  is  entirely  distinct  and 
separate  from  those  already  described.  It  usually  moves 
in  an  easterly  or  north  of  easterly  direction,  at  a  rate  of 
from  300  to  500  miles  a  day.  A  large  number  of  our 
storms  begin  in  the  Canadian  Northwest,  and  these  may 
cross  the  Great  Lakes  and  appear  a  day  or  so  later  over 
the  Eastern  states. 

The  cause  of  this  onward  passage  of  a  storm  across 
the  country  is  not  yet  clearly  understood,  but  it  seems 
to  be  intimately  associated  with  the  general  circulation 
of  the  atmosphere  and  probably  derives  its  energy  from 
the  same  source  as  the  latter. 

Rain  or  snow  at  the  storm  center.  Another  fact 
connected  with  a  storm  may  now  be  understood.  The  air 
that  moves  into  the  heated  area  is  more  or  less  saturated 
with  water  vapor,  and  as  this  moisture-laden  air  ascends 
into  the  colder  air  above,  the  vapor  becomes  condensed 
into  water  and  falls  to  the  earth.  Frequently  it  rains 
or  snows  near  the  storm  center. 

Because  of  these  two  reasons  the  storm  center  is  the 
area  of  low  barometer. 

The  barometer  and  the  storm  center.  There  are  two 
reasons  why  the  pressure  of  the  air  at  the  center  of  a 


The  Weather  211 

cyclonic  storm  is  less  than  that  of  the  air  surround- 
ing it : 

(1)  In  the  beginning,  at  least,  the  storm  center  is  a 
heated  area,  and  the  air  there  is  lighter  than  the  air 
which  surrounds  it. 

(2)  The  air  is  ascending  and  therefore  the  pressure 
below  it  must  decrease. 

What  will  the  weather  be  tomorrow?  The  barometer 
will  help  us  to  answer  this  question,  but  we  must  under- 
stand that  the  mere  height  of  the  mercury  in  the  barom- 
eter tells  us  little  or  nothing  about  the  weather.  It  is 
a  careful  study  of  the  changes,  or  ups  and  downs  of  the 
barometer,  that  will  enable  us  to  judge  what  the  cor- 
responding changes  in  the  weather  will  be.  General 
conclusions  may  be  drawn  from  three  possible  condi- 
tions : 

(1)  A    rising    barometer    generally     precedes     fair 
weather. 

(2)  A  falling  barometer  usually  precedes  stormy  or 
bad  weather. 

(3)  A  steady  or  stationary  barometer  usually  indicates 
settled  weather. 

How  the  weather  is  studied.  If  now  we  bear  in  mind 
the  fact  that  what  we  call  the  weather  depends  very 
largely  upon  changes  of  pressure  and  temperature  in 
the  atmosphere,  we  shall  understand  how  the  barometer 
and  the  thermometer  are  used  in  forecasting  the  weather. 
This  is  the  work  of  the  Weather  Bureau,  which  is 
attached  to  the  United  States  Department  of  Agricul- 
ture at  Washington. 


212  Science  for  Beginners 

The  Weather  Bureau.  The  United  States  Weather 
Bureau  was  organized  for  the  purpose  of  giving  warning 
to  sailors  on  the  high  seas  or  the  Great  Lakes  of  approach- 
ing dangerous  storms,  and  to  farmers  and  others  of 
threatening  rains,  floods,  cold  waves,  or  destructive 
frosts.  Hundreds  of  thousands  of  dollars  are  saved 
every  year  by  these  warnings.  In  several  hundred  lo- 
calities distributed  over  the  whole  country  are  stationed 
observers  who  take  observations  at  the  same  actual 
time  of  day  and  telegraph  their  reports  to  Washington. 
These  reports  cover  temperature,  barometric  pressure, 
the  percentage  of  moisture  in  the  atmosphere,  direction 
of  wind,  and  whether  it  is  clear  or  cloudy  or  raining  or 
snowing.  The  facts  thus  reported  are  entered  upon  a 
map,  copies  of  which  are  reproduced  on  a  small  scale  and 
sent  to  a  great  many  post  offices  and  telephone  exchanges 
in  the  country  and  published  in  many  of  our  daily  papers. 

Exercise  u.  Get  from  the  Weather  Bureau  office  in  your 
city  or  from  the  Weather  Bureau  at  Washington  the  weather 
reports  for  several  consecutive  days  and  make  a  study  of 
them.  On  these  maps  lines  are  drawn  through  all  places 
having  the  same  barometric  pressure.  These  lines  are 
called  isobars.*  Other  lines  which  pass  through  the  places 
having  the  same  temperature  are  called  isotherms.* 

A  study  of  the  weather.  Study  the  weather  yourself 
and  make  notes  of  what  you  observe.  Watch  the 
changes  in  temperature,  direction  of  the  wind,  kinds  of 
clouds,  rain,  or  snow ;  and,  if  you  have  a  chance  to  ob- 
serve a  barometer,  see  how  it  changes  as  the  areas  of 
low  and  high  barometer  pass  over  your  locality. 


The  Weather  213 

A  review  of  what  has  been  learned  about  storms  may 
be  made  by  the  aid  of  the  maps  which  follow. 

Figures  126-128  show  the  air  pressure,  temperature, 
and  winds,  over  the  United  States  on  three  successive 
days.  The  solid  lines  are  isobars,  showing  differences 
in  air  pressure  of  one  tenth  of  an  inch,  —  the  lower  the 
figure,  the  less  the  air  pressure  (29  inches  representing 
a  lower  pressure  than  29.8  inches). 

By  reference  to  the  three  maps  which  are  given  here 
you  will  be  able  to  answer  the  following  questions  for 
each  of  the  three  days : 

Exercise  1 1 .  How  does  the  temperature  vary  in  the  differ- 
ent states  ?  Where  were  the  high-pressure  areas  ?  In  what 
direction  was  the  wind  blowing  in  these  areas  ?  Where  were 
the  areas  of  low  pressure?  the  storm  centers?  How  was 
the  wind  blowing  in  these  areas? 

Exercise  12.  In  Figure  126  a  storm  is  central  over 
northern  Texas.  How  far  has  the  storm,  the  area  of  low 
pressure,  progressed  by  the  end  of  24  hours  ?  Over  what 
states  has  it  passed  ?  Through  how  many  miles  ?  At  what 
rate  per  hour?  In  what  direction  has  it  gone?  Where 
was  it  the  day  following  this?  When  did  it  reach  the 
Atlantic  seaboard?  Where? 

Direction  of  the  wind  in  a  storm  and  after  the  storm 
passes.  Notice  that  the  wind  is  blowing  from  all 
directions  toward  the  storm  center.  With  this  in  mind 
you  can  understand  why  it  is  that  the  wind  changes  to 
the  opposite  direction  when  the  storm  passes  over. 
When  the  wind  changes,  of  what  do  you  take  it  to  be 
a  sign? 


214 


Science  for  Beginners 


The  Weather 


215 


2l6 


Science  for  Beginners 


CHAPTER  TWENTY-TWO 

MATTER  AND   MOTION 

IN  the  early  chapters  of  this  book  you  studied  the 
subject  of  matter.  You  learned  that  matter  is  any- 
thing that  occupies  space,  that  possesses  form,  dimen- 
sions,* and,  especially,  weight.  You  learned  some  of  the 
properties  of  matter,  —  malleability,  ductility,  hardness, 
indestructibility,  and  so  forth. 

Exercise  i.  Make  a  careful  review  of  Chapters  Three, 
Four,  and  Five. 

In  these  chapters  you  learned  to  make  a  distinction 
between  matter  and  non-matter,  between  the  material  and 
the  immaterial.  The  word  "  matter "  has  grown  in 
your  mind  until  it  has  come  to  include  all  the  objects 
that  your  eyes  can  see  or  that  your  other  senses  can  bring 
to  your  attention,  —  the  animals  and  plants  that  live 
upon  the  earth's  surface,  the  water  that  covers  so  large 
a  part  of  that  surface,  the  air  or  atmosphere  that  sur- 
rounds it,  the  clouds  that  float  in  the  sky,  and  the  sun, 
moon,  and  stars  of  the  solar  system.  This  is  the  material 
world,  the  universe  of  matter.  Of  matter  you  have 
asked,  what  is  it?  You  have  studied  matter  by  the 
method  of  experiment. 

Motion.  There  are  other  facts  of  importance  about 
matter  still  to  be  learned.  Perhaps  you  have  not  thought 
of  it,  but  the  world  in  which  we  live  is  most  wonderful, 
in  the  fact  that  everything  in  it  is  in  constant  motion. 
The  rivers  flow  to  the  sea;  the  winds  move  over  the 
surface  of  the  earth ;  the  waters  of  the  ocean  are  stirred 
by  currents  and  tides;  and  waves  of  motion  are  sent 
through  the  solid  crust  of  the  earth  itself  by  every  moving 

217 


2i8  Science  for  Beginners 

train  or  wagon  and  by  every  blow  from  the  feet  of  animals 
or  men.  Even  when  we  sit  quietly  in  a  comfortable 

chair  at  home  we  are 
not  at  rest,  but  are 
rapidly  moving  through 
space;  for  the  earth 
is  turning  on  its  axis 
and  by  this  motion 
is  carrying  everything 
upon  it  through  a  dis- 
tance equal  to  its  cir- 
cumference every  24 

FIG.    129.    Matter   is    powerless    to    move    hours,  while  at  the  Same 

itself.    A  house  erected  a  hundred  years  ago    , .  •,,       ,  M1 

may  be  fourld  still  standing  in  the  same  place,     time,  With  Still    greater 

velocity,  it  is  rushing 

onward  in  its  long  journey  around  the  sun.  Strange, 
is  it  not,  that  this  is  so  quietly  done  and  at  such  a 
uniform  rate  that  nothing  on  the  earth  is  disturbed  and 
we  do  not  realize  that  we  are  in  rapid  motion ! 

Some  questions  to  be  answered.  What  is  the  proof 
that  the  earth  does  rotate*  on  its  axis  ?  Go  out  of  doors 
at  night  for  your  answer.  Why  do  the  sun  and  the 
moon  seem  to  rise  in  the  east  and  set  in  the  west  ?  How 
long  a  journey  do  we  take  every  day  because  of  the  rota- 
tion of  the  earth?  How  far  do  we  travel  every  hour? 
every  minute?  Have  you  ever  traveled  a  thousand 
miles  by  train  or  boat  ?  How  long  does  it  take  to 
travel  a  thousand  miles  by  an  express  train?  Ask  the 
agent  at  the  railroad  station  for  a  folder  of  one  of  the 
great  trunk  lines  and  find  the  answer  to  this  question. 


Matter  and  Motion 


219 


Why  does  the  moon  rise  about  50  minutes  later  every 
night?  At  what  time  of  day  do  you  first  see  the  new 
moon  ?  Where  ?  When  do  you  first  see  the  full  moon  ? 
Where?  Go  to  the  library  and  find  out  how  long  a 
trip  the  earth  makes  about  the  sun  and  how  much  time 
it  takes  to  make  a  complete  revolution.* 

Even  after  answering  these  questions  you  have 
not  considered  all  the  movements  of  the  earth;  for 
the  earth  and  the  other  planets  (do  you  know  their 
names?)  are  all  following  the  sun,  "  while  the  sun  with 
his  whole  retinue*  flies  with  incredible  velocity  through 
space." 

Matter  unable  to  move  itself.  Matter  is  inert,* 
inactive,  powerless  to  move  itself.  By  itself  it  is  quite 
helpless  to  change  its  position,  to  move  about.  Of  this 
fact  you  can  find  many  illustrations. 

A  rock  lying  in  a  meadow  cannot  move  itself.  A 
tree  blown  down  in  a  forest  by  a  hurricane  lies  where  it 
falls.  A  house  or  barn  erected  possibly  a  hundred 
years  ago  may  be  found 
still  standing  in  the  same 
place. 

Objects  like  these  will 
never  move  by  their  own 
power.  Of  all  matter  we 
must  say  that  matter  at 
rest  will  remain  at  rest 
until  acted  upon  by  some 
force  outside  itself.  This 
is  true  of  all  forms  of  mat- 


FIG.  130. 


Why  does  not  the  coin  move 
with  the  card? 


22o  Science  for  Beginners 

ter ;  the  earth,  air,  water,  rocks,  and  even  machines  like 
automobiles  and  aeroplanes  will  lie  still  and  helpless 


FIG.  131.    Matter  has  no  power  to  stop  itself.    A  body  in  motion  will  remain 
in  motion  until  stopped  by  an  outside  force. 

forever  unless  they  are  pushed  or  pulled  into  motion  by 
some  outside  force. 

Exercise  2.  Balance  a  card  on  the  ball  of  your  finger, 
and  place  a  coin  upon  the  card.  With  the  finger  of  the 
other  hand  snap  the  edge  of  the  card  quickly.  After  a  few 
trials  you  will  be  able  to  snap  the  card  away  and  leave  the 
coin  lying  on  your  finger. 

You  have  exerted  a  greater  force  upon  the  card  than 
upon  the  coin.  Consequently  the  card  moves  while  the 
coin  remains  at  rest. 

Exercise  3.'  Vary  the  method  of  making  the  last  experi- 
ment by  laying  the  card  upon  the  top  of  a  small  tumbler. 
The  coin  will  fall  into  the  tumbler. 

Moving  bodies  cannot  stop  themselves.  As  matter 
has  not  the  power  to  set  itself  in  motion,  so  matter  has 
no  power  of  itself  to  stop  when  once  it  is  set  in  motion. 


Matter  and  Motion 


221 


FIG.  132.  The  momentum,  or  strik- 
ing force,  of  the  hammer  drives  the 
nail  into  the  wood. 


It  will  go  on  moving  forever 
unless  acted  upon  by  some 
opposing  force.  For  exam- 
ple, take  a  stone  that  is  set 
rolling  down  hill.  It  is  quite 
plain  that  it  possesses  no  power 
of  its  own  to  stop  in  its  mad 
rush  down  the  hill.  A  train 
that  is  running  at  great  speed 
tends  to  fly  onward,  and  it  can  be  brought  to  a  stop  only 
by  applying  great  force  to  the  brakes  for  a  considerable 
time.  When  an  iceberg  is  sighted  in  front  of  an  ocean  liner 
the  engines  are  at  once  reversed,  but  the  ship  continues 
on  its  course  for  a  time  in  spite  of  the  action  of  the  engines. 
A  person  falling  through  the  air  is  in  a  position  to  under- 
stand this  helplessness  of  matter  to  stop  itself.  He 
cannot  do  anything  to  check  the  motion  of  his  body, 
for  he  is  in  the  grasp  of  forces  outside  himself. 

Exercise  4.  Draw  a  line  upon  the  earth  and  run  across  it 
as  rapidly  as  possible.  As  soon  as  you  cross  the  line,  stop 
running.  Do  you  have  a  tendency  to  keep  moving? 

Why  is  a  train  hard  to  start  but  easy  to  keep  moving 
after  it  is  started? 

What  happens  to  a  person  who  is  standing  in  a  moving 
train  or  street  car  which  is  suddenly  stopped? 

Momentum.  By  "  momentum  "  is  meant  the  quantity 
of  motion,  or,  as  it  is  sometimes  called,  the  striking  force 
of  a  moving  body.  The  momentum  of  a  body  equals  its 
mass  (the  weight)  multiplied  by  its  velocity  (the  rapidity 
of  its  motion). 


222 


Science  for  Beginners 


FIG.  133.  Diagram  illustrating 
why  there  is  friction  when  one  body 
moves  on  another. 


If  you  have  the  last  statement  clear  in  your  mind, 
you  will  understand  that  a  small  body  moving  very  fast 

may  have  the  same  striking 
force  as  a  larger  body  which 
is  moving  more  slowly.  In 
other  words : 

The  greater  the  weight  the 
greater  the  momentum;  the 
less  the  weight  the  less  the 
momentum. 

The  greater  the  velocity  the  greater  the  momentum; 
the  less  the  velocity  the  less  the  momentum. 

Illustrations  of  momentum.  A  huge  iceberg,  although 
moving  very  slowly,  has  a  tremendous  momentum,  or 
striking  force,  upon  a  vessel  with  which  it  comes  into 
contact. 

A  large  ocean  steamship,  although  moving  very  slowly, 
may  strike  the  wharf  with  great  force  if  the  pilot  is  not 
careful. 

Find  an  illustration  of  the  fact  that  a  body  has  more 
momentum  when  it  is  moving  rapidly  than  when  it  is 
moving  slowly. 

Does  a  heavy  body  have  more  or  less  momentum  than 
a  lighter  body  moving  with  the  same  speed  ?     Illustrate. 
Can  you  strike  harder  with  a  hammer  or  with  a  lead 
pencil?    Why? 

Motion  destroyed  by  friction.  In  spite  of  the  fact 
that  moving  bodies  cannot  stop  themselves,  objects 
that  we  set  in  motion  do  come  to  rest  without  our  help. 
Why  do  they  not  keep  moving  forever? 


Matter  and  Motion 


223 


FIG.  134.    Rolling  friction  is  less  than  sliding  friction. 

Exercise  5.  Lay  a  large  book  or  other  heavy  object 
on  a  desk  or  on  the  floor  and  draw  it  along.  Does  something 
resist  the  movement  of  the  book  ?  Start  the  book  in  motion 
and  let  it  go.  Does  it  stop? 

Exercise  6.  Weigh  a  brick  with  a  spring  balance.  Tie  a 
string  around  the  brick  and  with  the  balance  attached  to  the 
string  draw  the  brick  along  the  floor.  Take  the  reading  of 
the  balance.  Explain  the  difference  in  the  two  readings. 
Does  it  make  any  difference  whether  the  brick  is  laid  flat- 
wise or  on  its  edge  ? 

Friction.  The  resistance  which  always  opposes  the 
movement  of  one  body  on  another  is  called  friction,  and  in 
many  cases  this  is  the  force  which  brings  moving  bodies 
to  a  stop.  When  we  roll  a  ball  on  the  ground,  its  motion 
is  checked  by  the  friction  with  the  ground.  If  it  is  rolled 
on  the  sidewalk  it  will  go  farther,  because  there  is  less 
friction  on  the  sidewalk  than  on  the  rough  earth.  If  it  is 
rolled  on  the  ice  it  will  go  still  farther,  because  the  ice  is 
very  smooth,  and  there  is  little  friction  between  the  ball 
and  the  ice.  In  all  three  cases,  however,  the  motion  of 
the  ball  is  being  opposed;  but  if  the  opposing  force 
could  be  removed  the  ball  would  roll  on  forever. 


224  Science  for  Beginners 


FIG.  135.     Some  devices  to  lessen  friction. 

Friction  useful.  While  friction  always  opposes  motion 
and  results  in  loss  of  motion,  it  should  be  noticed  that  in 
many  cases  friction  is  very  useful  to  us.  Standing 
upon  the  ground  or  the  floor  is  only  possible  because 
of  the  friction  between  our  feet  and  the  ground.  With- 
out friction  we  could  neither  walk  nor  run.  Without 
friction  we  could  not  turn  a  door  knob  and  would  have 
the  greatest  difficulty  in  holding  anything  in  our  hands ; 
nails  and  screws  would  hold  nothing  together;  a  loco- 
motive could  not  start  a  train. 

Practical  questions.  Is  there  less  friction  when  a 
body  is  dragged  or  when  it  is  rolled  along  the  ground? 
Of  what  use  are  the  wheels  on  a  wagon?  Why  do  we 
oil  the  bearings  of  our  bicycles  ?  Why  does  a  ball-bearing 
lawn  mower  run  more  easily  than  one  without  ball  bear- 
ings ?  Why  is  a  racing  automobile  made  pointed  at  the 
front  end? 

A  moving  body  tends  to  travel  in  a  straight  line.  A 
third  fact  about  matter  in  motion  is  that  a  body  in  motion 
will  keep  moving  in  a  straight  line  unless  acted  upon  by 
some  outside  force. 

Exercise  7.  Run  along  the  side  of  the  house  as  rapidly  as 
possible,  turn  the  corner,  and  continue  running  along  the 


Matter  and  Motion  225 

wall  of  the  house.     Do  you  have  a  tendency  to  keep  going 
in  the  same  direction  instead  of  turning  round  the  corner? 


FIG.  136.    A  moving  body  tends  to  travel  in  a  straight  line. 

Why  is  a  boy  who  is  standing  still  able  to  dodge 
another  boy  who  is  running  rapidly  at  him?  Why 
must  a  trolley  car  run  more  slowly  when  it  approaches 
a  sharp  curve? 

Exercise  8.  Make  a  sling  like  the  one  shown  in  Figure 
136.  Select  a  safe  place  for  your  experiment,  then  fit  a 
stone  into  the  sling,  whirl  it  about  your  head,  and  release 
one  of  the  strings.  Does  the  stone  continue  to  move  in  a 
circle,  or  does  it  travel  off  in  a  straight  line  when  it  leaves 
the  sling?  Why? 

Force  the  cause  of  motion.  What  is  it  that  sets  objects 
in  motion?  How  can  their  motion  be  stopped  or  its 
direction  changed?  These  are  questions  that  we  must 
answer  before  we  can  understand  many  of  the  things  we 
see  and  do  every  hour. 

You  may  change  the  position  of  a  book  on  your  table 
by  a  push  or  a  pull.  In  either  case  you  have  exerted  a 
force  upon  the  book.1  If  the  book  is  very  heavy,  the 
force  may  not  be  sufficient  to  cause  motion,  but  we  can 

1  A  force  is  a  push  or  a  pull  exerted  by  one  body  of  matter  upon 
another  body. 


226 


Science  for  Beginners 


FIG.  137- 


still  say  that  the  force  tends 
to  produce  motion.1 

Again,  the  book  might  be 
in  motion  and  the  force  might 
change  the  direction  of  the 
motion  or  bring  the  book  to 
rest.  We  may  therefore  say 
that  a  force  is  that  which  tends 
to  produce  or  change  motion. 
Let  us  study  a  force  whose 
effects  are  familiar  to  us  all. 

The  force  of  gravity.  Once 
upon  a  time  a  great  philoso- 
pher, Sir  Isaac  Newton,  no- 
ticed an  apple  falling  from 
a  tree  to  the  earth.  His 
mind  was  aroused  to  find  a 


reason  for  this.  When  an  apple  is  separated  from  the 
twig  on  which  it  grows,  why  does  it  fall  to  the  earth? 
What  causes  this  motion?  Why  does  the  apple  not  re- 
main in  the  air,  or  move  upward  away  from  the  earth? 
After  a  long  study  of  these  and  other  questions,  Sir 
Isaac  announced  that  an  apple  falls  to  the  earth  because 
every  particle  of  matter  in  the  universe  has  an  attrac- 
tion  for  every  other  particle.  Think  carefully  what 
this  means;  it  is  a  most  astonishing  statement.  All 
bodies  of  matter  pull  other  bodies  of  matter  toward 
themselves.  The  earth  attracts  the  apple  and  it  falls; 

1  One  little  girl  when  asked  the  meaning  of  this  sentence  replied, 
"  The  force  tries  to  produce  motion." 


Matter  and  Motion  227 

but  the  apple  also  attracts  the  earth,  which  moves  up 
to  meet  the  apple.  This  attractive  force  is  called 
gravitation.  When  this  force  is  exerted  by  the  earth, 
it  is  called  the  force  of  gravity.  We  measure  the  effects 
of  the  force  of  gravity  in  pounds.  With  how  much  force 
does  the  earth  draw  you  downward?  Give  the  answer 
in  pounds. 

Conclusion.  We  have  learned  in  this  chapter  that 
much  of  the  matter  in  the  universe  is  in  motion ;  that 
matter  in  itself  is  inert  and  helpless  and  that  all  motion 
and  changes  in  motion  are  due  to  outside  forces  which 
act  on  the  matter.  We  have  learned  what  is  meant  by 
momentum,  friction,  and  the  force  of  gravity,  and  have 
learned  something  of  their  importance  in  our  lives.  In 
every  movement  that  you  make ;  in  every  piece  of  work 
that  you  do ;  and  in  all  the  activity  and  motion  of  the 
people  and  things  about  you  scores  of  illustrations  of 
the  facts  and  laws  that  we  have  discovered  will  be  seen. 
Can  you  learn  to  read  this  book  of  motion  that  is  con- 
stantly opened  before  your  eyes?  A  good  scientist 
should  be  learning  from  it  day  by  day. 


CHAPTER  TWENTY-THREE 

MOTION  TO  AND  FRO 


Go  out  of  doors  and  ob- 
serve the  objects  that  are  in 
motion.  Notice  that  some 
of  them  —  like  the  trees  and 
their  branches  swaying  in  the 
wind,  the  heads  of  grain  and 
the  flowers  swinging  on  their 
stems,  the  telephone  wires 
hanging  on  their  poles  — 
move  back  and  forth  but 
always  come  to  rest  in  the 
same  place.  These  latter 
objects  have  vibratory  mo- 
tion, or,  to  use  another  expres- 
sion, a  to-and-fro  motion  — • 
a  very  important  kind  of 
motion  that  is  different  from 
FlG'  I38>  any  of  the  examples  of  mo- 

tion which  were  studied  in  the  last  chapter. 

The  waves  of  the  sea,  the  light  that  comes  to  our 
eyes,  the  sound  that  strikes  our  ears,  and  the  waves  that 
carry  the  wireless  telegraph  messages  across  the  sea  are 
all  the  result  of  motion  of  this  kind. 

The  pendulum  and  its'  vibration.  A  pendulum  con- 
sists of  a  weight  so  suspended  as  to  move  freely  (Fig. 
138).  The  distance  from  the  point  of  suspension  to 
the  center  of  the  weight  is  the  length  of  the  pendu- 
lum. Let  us  study  the  swinging  to  and  fro  of  a  pendu- 

228 


Motion  To  and  Fro  229 

lum,  for  in  it  we  shall  find  a  good  example  of  vibratory 
motion. 

Exercise  i.  Arrange  a  pendulum  (Fig.  138)  and  start  it 
swinging  back  and  forth. 

A  complete  vibration  is  a  swing  from  one  side  of  the 
arc*  to  the  other  and  back  again  —  from  B  to  D  and 
back  again  to  B. 

A  simple  vibration  is  a  swing  from  one  side  of  the  arc 
to  the  other  —  from  B  to  D. 

The  amplitude  of  the  vibration  is  one  half  of  the  simple 
vibration  —  from  A  to  B. 

The  period  of  the  vibration  is  the  time  required  to 
make  one  simple  vibration. 

Exercise  2.     Study  the  vibrations  and  notice  carefully: 

(1)  That  they  all  start  from  a  position  of  rest;  i.e.,  the 
pendulum  is  standing  still  at  the  moment  when  it  starts 
its  swing  through  the  arc. 

(2)  That  the  motion  is  faster  and  faster  until  the  pendulum 
reaches  the  point  where  the  motion  is  most  rapid  —  the  bot- 
tom, of  the  arc. 

(3)  That  after  this  the  pendulum  goes  more  and  more 
slowly  until  it  again  comes  to  a  stop,  when  it  turns  back  to 
repeat  the  motion  as  before. 

(4)  That  when  the  pendulum  comes  to  rest,  the  cord 
takes  a  vertical  position,  with  the  ball  as  near  to  the  center 
of  the  earth  as  it  can  be.     Why? 

You  will  understand  that  it  is  the  force  of  gravity 
that  pulls  the  ball  of  the  pendulum  downward  in  its 
path.  When  it  is  once  set  in  motion,  it  cannot  stop  of 
itself.  Its  momentum  carries  it  past  its  point  of  rest 


230 


Science  for  Beginners 


FIG.  139.  Pendulums  of  the 
same  length  vibrate  in  the  same 
time. 


to  the  other  side  of  the  arc,  from 
which  it  falls  back  in  the  next 
swing. 

Exercise  3.  Allow  the  pendu- 
lum to  vibrate,  and  notice  that 
its  swing  becomes  shorter  and 
shorter,  and  that  finally,  like  a 
swing,  the  "  old  cat  dies  "  and  the 
vibrations  cease. 

The   friction  of   the  air  and 
the  friction  at  the  point  of  sus- 
pension will  little  by  little  de- 
stroy the  motion  of  the  pendu- 
lum and  finally  bring  it  to  rest. 
The  first  law  of  the  pendulum.    There  are  several 
laws  of  the  pendulum,  and  the  best  way  to  learn  them  is 
by  the  method  of  experiment. 

Exercise  4.  With  watch  in  hand,  count  the  number  of 
vibrations  that  a  pendulum  will  make  in  10  seconds. 

Repeat  the  experiment  several  times,  but  each  time  cause 
the  pendulum  to  vibrate  through  a  different  arc  or  amplitude. 

From  this  experiment  you  will  learn  the  surprising 
fact  that  a  given  pendulum  will  always  vibrate  in  the 
same  period  of  time  no  matter  what  the  amplitude  of 
the  vibration  may  be ;  that  is,  whether  the  pendulum 
makes  a  long  swing  or  a  short  one,  it  takes  the  same 
time  for  the  swing.  This  is  the  great  and  most  important 
law  of  the  pendulum. 

How  the  first  law  of  the  pendulum  was  discovered. 
As  he  sat  in  the  Cathedral  of  Pisa,  Galileo,  the  famous 


Motion  To  and  Fro 


231 


*he 

faster 


the 


Italian  philosopher,  noticed  the  swing- 

ing to    and  fro  of  a  lamp  which  was 

suspended  from  the  ceiling.     It  seemed 

to  him  that  the  motion  was  very  reg- 

ular,   although    sometimes    the    lamp 

would   swing   through   a  longer   space 

than    at   other  times.     He    compared 

the  time  of  the  swing  of  the  lamp  with 

the  beat  of  his  own  pulse,  and  by  this 

curious  method  made  a  great  discov- 

ery.    He  found  that  the  lamp  always  FIG.  140.  The  shorter 

took  exactly  the  same  time  to  swing 

-  c  -  ? 

to    and    fro.     Here     was     an     exact 

method  of  measuring  time,  and  it  has  led  to  some  very 

important  inventions. 

A  second  law  of  the  pendulum.  Does  it  make 
any  difference  whether  the  ball  of  a  pendulum  is 
heavy  or  light?  Whether  it  is  made  of  wood  or  of 
metal  ? 

Exercise  5.  Take  two  balls  of  equal  size  but  of  different 
materials,  one  of  wood  and  the  other  of  iron  or  lead.  An 
apple  and  a  stone  of  equal  size  may  be  used.  Hang  them 
side  by  side  with  cords  of  the  same  length  (Fig.  139).  Hold 
one  in  each  hand,  draw  them  out  to  the  same  distance,  and 
let  them  go.  Do  they  get  back  to  your  hands  at  the  same 
time?  Determine  the  period  or  the  time  of  vibration  by 
counting  the  number  of  vibrations  in  each  case  in  20  seconds. 
Make  a  number  of  such  observations  and  take  the  average 
of  the  periods. 

Try  other  weights,  always,  however,  keeping  the  two 
pendulums  of  the  same  length.  Would  the  resistance  of  the 


232 


Science  for  Beginners 


air  make  a  difference  in  the  result  if  the  weights  were  of 

different  sizes? 

This  experiment  has  given  us  the  second 
law  of  the  pendulum :  that  pendulums  of 
the  same  length,  but  of  different  weights 
and  materials,  vibrate  in  the  same  time. 

A  third  law  of  the  pendulum.  If  the  size 
and  the  weight  of  a  pendulum  have  nothing 
to  do  with  the  rate  of  its  vibration,  how  can 
one  pendulum  be  made  to  vibrate  faster  than 
another  ? 

Exercise  6.  Take  two  weights  of  the  same 
material  and  size,  and  cords  of  different  length 
(Fig.  140).  Which  moves  the  faster?  Is  it 
true  that  the  shorter  the  pendulum  the  faster 
it  vibrates  ?  This  is  the  third  law  of  the 
pendulum,  and  it  is  an  important  one. 

What  change  is  made  in  the  pendulum  of 
a  clock  that  runs  too  slow  ?  of  one  that  runs 

FIG.  141.    The    t00  fast? 

pendulum  and       A   wonderful    instrument.     One   of    the 

escapement  of  mo^  important  inventions  ever  made  is  that 

a  clock.    A    is  F 

the     "escape  piece    of    apparatus    known    as  the  clock, 
wheel"  and  B  Trains  run  by  it;  ships  sail  by  it;  we  rise 

the  "anchor."  ,   J  \  ,        .       J_ 

and  eat  and  go  to  bed  by  it.  It  measures 
off  time  for  us  so  that  we  can  say,  "  At  such  an  hour 
tomorrow  I  shall  be  at  such-and-such  a  place  "  and  the 
person  who  is  to  meet  us  will  know  exactly  when  to 
expect  us  to  appear. 
The  clock  is  an  instrument  whose  second  hand  will 


Motion  To  and  Fro 


233 


divide  the  day  into  86,400  parts ;  an 
instrument  that  will  record  accurately 
the  flow  of  the  immaterial  stream  of 
time,  which  we  cannot  see,  hear,  touch, 
taste,  or  smell.  On  what  principle 
does  this  instrument  work? 

Exercise  7.  Procure  an  old  clock, 
remove  the  face,  and  watch  the  move- 
ments of  the  various  parts.  Notice  the 
regular  swing  of  the  pendulum  and  ob- 
serve that  when  the  pendulum  is  at  rest 
none  of  the  wheels  are  moving.  Review 
Exercises  4  and  6. 

Since  the  movement  of  the  wheel 

,  ,  , ,  -.  _, ,  ,         FIG.    142.      Apparatus 

depends  on  the  swinging  of  the  pendu-  to  demonstrate  longi- 
lum,  it  is  evident  that  the  clock  keeps  tudinai  and  torsionai 
correct  time  because  each  swing  of  the 
pendulum  back  and  forth  is  made  in  a  certain  exact 
period  of  time.  That  is,  it  is  the  pendulum  that  meas-. 
ures  off  the  time,  and  the  hands  of  the  clock  only  record 
the  number  of  swings  that  the  pendulum  has  made. 

Exercise  8.  Examine  the  clock  further  to  see  how  the 
swinging  of  the  pendulum  regulates  the  movements  of  the 
wheels  and  hands  of  the  clock.  The  spring  and  a  "  train 
of  gears  "  (not  shown  in  the  figure)  drive  the  escape  wheel 
(A).  At  each  vibration  the  escape  wheel  gives  a  slight 
push  to  the  pallets  (the  teeth  on  the  ends  of  the  anchor,  B) 
and  this  is  communicated  to  the  pendulum  through  C. 
In  this  way  the  pendulum  is  kept  in  motion. 

Other  kinds  of  vibratory  motion.  The  pendulum 
vibrates  to  and  fro  across  the  direction  of  the  string  by 


234  Science  for  Beginners 

which  it  is  hung.  Its  vibrations  are  therefore  called 
transverse*  vibrations.  Examples  of  other  kinds  of 
vibrations  are  shown  by  the  following  experiments : 

Exercise  9.  Go  to  the  toy  store  and  buy  a  small  wooden 
ball  with  a  piece  of  elastic  rubber  cord  attached  to  it.  Suspend 
the  ball  from  some  convenient  place  so  that  it  is  at  least  a 
foot  above  the  floor.  With  the  hand  pull  the  ball  directly 
downward  and  then  let  it  go.  It  will  vibrate  up  and  down, 
to  and  fro,  in  the  direction  of  the  cord.  Are  these  vibrations 
made  in  equal  times?  Compare  Exercise  4. 

This  kind  of  vibration  is  called  a  longitudinal*  vibra- 
tion, since  it  takes  place  in  the  direction  of  the  length  of 
the  string. 

Exercise  10.  Suspend  a  ball  by  a  stiff  wire.  Stick  a  pin 
into  the  ball,  or  paste  a  pointed  paper  upon  it,  so  that  when 
the  ball  is  at  rest  the  pin  or  paper  is  parallel  with  the  floor. 
Now  turn  the  ball  partly  around  so  as  to  twist  the  wire.  Let 
it  go,  and  notice  the  pin  as  it  swings  to  and  fro. 

This  kind  of  vibration  is  called  a  torsional*  vibration. 
It  is  not  seen  so  often  as  the  other  two  kinds. 

Conclusion.  We  have  learned  what  the  word  "vibra- 
tion "  means ;  we  have  learned  to  recognize  examples  of 
vibratory  motion  all  about  us,  and  to  know  some  of  the 
laws  that  govern  them.  This  knowledge  is  extremely 
valuable  in  itself,  and  it  will  enable  us  to  glimpse  vibra- 
tions that  are  more  minute  than  these  and  therefore  more 
difficult  to  see.  It  will  also  help  us  to  believe  in  the  vi- 
bratory motion  of  the  molecules  of  matter  which  cannot  be 
seen  with  our  natural  eyes.  Thus  we  shall  finally  learn 
the  method  by  which  the  scientist  "  sees  the  invisible." 


CHAPTER  TWENTY-FOUR 

SOUND 


FIG.  143.    Only  the  song  which  drops  back  to  earth  tells  the  watcher  that  the 
little  musician  is  still  on  the  wing. 

IN  England  there  is  a  small  bird  called  a  skylark,  that 
is  a  wonderful  singer.  It  rises  through  the  air,  pouring 
a  flood  of  melody  from  its  throat,  and  continues  to  ascend 
until  it  vanishes  from  sight  and  only  the  song  which 
drops  back  to  earth  tells  the  watcher  that  the  little 
musician  is  still  on  the  wing. 

What  is  it  that  comes  from  the  throat  of  a  bird  when 
we  hear  it  sing?  Is  it  matter?  Is  it  motion?  Or  is  it 
something  else?  And  whatever  it  is,  how  does  it  travel 
to  our  ears?  Let  us  investigate  this  thing  that  we 
call  sound,  and  see  if  we  can  learn  what  it  is  and  how  it 
comes  to  us. 

235 


236  Science  for  Beginners 

Exercise  i.  Fill  a  good-sized  tumbler  partly  full  of  water 
and  gently  rub  the  upper  rim  of  the  glass  with  the  ball  of  your 
wet  finger.  Look  and  listen.  Observe  the  surface  of  the 
water  for  signs  of  vibrations. 

Exercise  2.  Gently  tap  the  prongs  of  a  tuning  fork 
upon  the  edge  of  the  table  and  bring  the  handle  down  upon 
the  table.  What  do  you  observe?  What  is  the  iron  of 
the  tuning  fork  doing  ?  Hold  a  knife  blade  to  the  side  of  the 
fork  and  notice  the  rapid  tap,  tap  of  the  fork  upon  the  knife. 
Have  you  discovered  a  to-and-fro  motion?  Tap  the  fork 
again  and  place  the  handle  between  your  teeth,  and  feel 
the  movement  going  on.  Hold  it  against  your  cheek  and 
feel  the  vibrations. 

Exercise  3.  Strike  a  bell  and  touch  the  finger  to  it. 
Suspend*  a  piece  of  cork  or  a  small  pith  ball  so  that  it 
will  touch  the  bell.  Do  you  hear  the  sound  of  the  bell  at 
the  same  time  that  you  see  the  vibratory  motion  of  the  bell  ? 
Does  the  sound  grow  fainter  as  the  vibrations  of  the  bell 
grow  less? 

Are  you  now  ready  to  believe  that  there  is  a  close 
relation  between  sound  and  vibration;  that,  indeed, 
sounds  are  produced  by  vibrations,  and  that  when  we 
begin  to  investigate  sound  we  at  once  find  ourselves 
dealing  with  the  same  kind  of  motion  that  we  studied 
in  the  last  chapter? 

Sound  transmitted  by  the  air.  We  have  learned  that 
sounds  are  produced  by  vibratory  bodies.  An  interest- 
ing experiment  will  show  that  sound  is  carried  by  the 
air. 

Exercise  4.  Suspend  an  electric  bell  in  a  bell  jar, 
running  the  wires  to  the  bell  through  a  rubber  stopper 


Sound 


237 


in  the  top  of  the  jar.1  Send 
a  current  of  electricity 
through  it,  and  the  sound 
of  the  bell  will  be  heard  by 
all. 

Now  place  the  jar  on  an 
air  pump  and  pump  the  air 
out  of  it.  The  sound  of  the 
bell  becomes  fainter  and 
fainter,  and  if  the  air  is  all 
removed  the  sound  can  no 
longer  be  heard. 

Sound  carried  by  other 
substances.  The  above 
experiment  shows  that 
sound  will  not  be  trans- 
mitted in  a  vacuum,*  but 
that  it  travels  through  the 
air.  Let  us  see  if  other  substances  will  transmit  sound. 

Exercise  5.  Place  the  ear  at  the  end  of  a  long  strip  of 
wood,  —  a  log,  a  fence  board,  or  a  fish  pole,  —  and  listen 
while  some  one  faintly  taps  or  scratches  the  other  end.  Does 
the  wood  carry  the  sound  ? 

Exercise  6.  Sometime,  when  bathing,  immerse  the 
head  in  water  and  let  another  person  who  is  stationed  at 
a  distance  strike  two  stones  together  under  the  water.  The 
sound  will  be  distinctly  heard. 

1  This  experiment  can  be  performed  with  an  alarm  clock  suspended  so 
that  it  will  not  touch  the  walls,  or  placed  on  a  piece  of  felt  as  shown  in 
Figure  144.  When  the  latter  method  is  employed  the  material  on  which 
the  clock  rests  conducts  the  vibrations  sufficiently  to  cause  the  sound  to 
be  heard  faintly. 


FIG.  144.    As  the  air  is  exhausted*  the 
sound  becomes  fainter  and  fainter. 


238 


Science  for  Beginners 


FIG.  145.    The  bell  sends  out  waves  in 
the  air. 


We  have  now  learned 
that  sound  travels  to 
the  ear  through  air, 
wood,  or  water.  That 
is,  sound  is  transmitted 
by  solids,  liquids,  and 
gases. 

What  sound  is. 
Strike  a  bell.  What  is 
it  that  comes  to  the 
ear  when  we  hear  the 
sound?  It  is  waves  of 
motion  in  the  air.  As 

the  bell  vibrates  back  and  forth  it  strikes  the  molecules 
of  the  air  and  sends  out  little  waves  in  the  air,  much 
as  waves  are  sent  out  in  the  water  of  a  pond  when  a 
stone  is  thrown  into  it.  When  these  waves  strike 
the  ear  they  start  messages  in  the  nerves  of  hearing, 
and  when  these  messages  reach  the  brain  we  hear  the 
sound. 

Can  you  now  explain  why  a  bell  gives  forth  no  sound 
when  it  rings  in  a  vacuum? 

To  estimate  the  velocity  of  sound.  Have  you  ever 
noticed  that  the  flash  of  a  gun  is  seen  before  the  report 
is  heard;  that  the  steam  from  a  locomotive  whistle  is 
seen  before  the  sound  is  heard ;  and  that  a  flash  of  light- 
ning may  reach  the  eye  some  seconds  before  the  thunder 
comes  to  the  ear?  If  we  know  the  distance  from  the 
ear  to  the  source  of  the  sound  and  at  the  same  time 
count  the  number  of  seconds  of  time  between  the 


Sound  239 

flash  and  the  report,  we  may  learn  the  velocity  of 
sound.1 

Exercise  7.  Let  two  boys  stand  at  a  known  distance 
apart,  say  a  quarter  or  a  half  of  a  mile.  Let  one  boy  fire 
a  gun  and  let  the  other  boy  with  a  watch  count  the  time  be- 
tween seeing  the  flash  or  smoke  of  the  gun  and  hearing  the 
report. 

The  same  experiment  can  be  worked  by  standing  at  a 
known  distance  from  a  railroad  track  and  finding  how  long 
it  takes  the  sound  to  reach  you  after  the  steam  from  the 
whistle  is  seen. 

Sound  travels  in  air,  at  ordinary  temperature,  about 
noo  feet  per  second.  In  water  at  a  little  above  the 
freezing  point  its  velocity  is  4677  feet  per  second. 

Exercise  8.  During  an  electrical  storm  hold  your 
watch  and  count  the  number  of  seconds  between  the 
flash  of  the  lightning  and  the  sound  of  the  thunder.  Sup- 
pose it  is  an  interval  of  10  seconds.  How  far  away  is  the 
thunder  ? 

The  pitch  of  sounds.  Some  sounds  have  a  low  pitch 
and  some  a  high  pitch.  Let  us  see  if  we  can  determine 
why  this  is  true. 

Exercise  9.  Let  some  pupil  bring  to  school  a  violin  or 
guitar,  or  any  other  stringed  instrument.  Draw  the  bow 
across  a  string  and  note  the  sound.  Fold  a  small  strip  of 
paper  and  hang  it  on  the  string ;  then  bow  the  string  again. 
Shorten  the  string  as  the  violinist  does  when  playing.  Is 

1  The  time  it  takes  for  the  light  to  travel  to  the  eye  may  be  disregarded 
in  this  problem  because  of  the  very  great  velocity  of  light  (page  283). 
The  time  taken  by  light  to  travel  a  distance  of  a  few  miles  is  only  a 
very  small  fraction  of  a  second, 


240  Science  for  Beginners 


FIG.  146.    Which  tuning  fork  will  give  forth  the  higher-pitched  note, 
and  why? 

the  sound  the  same  as  before?    Is  it  higher  or  lower? 
Shorten  the  string  still  more  and  note  the  sound. 

What  is  the  law  of  the  string  ?  The  shorter  the  string 
the  higher  the  tone.  Now  recall  the  law  of  the  pen- 
dulum, the  shorter  the  pendulum  the  more  rapid  the 
vibration.  Can  we  now  draw  an  inference  by  putting 
these  two  laws  together;  namely,  the  shorter  string 
vibrates  more  rapidly  and  thus  produces  the  higher 
tone?  That  is,  if  a  body  vibrates  rapidly  and  sends 
the  air  waves  against  the  ear  in  quick  succession,  the  pitch 
is  high ;  if  the  vibrations  are  slow  and  the  waves  strike 
against  the  ear  less  frequently,  the  pitch  is  lower. 

What  effect  does  tightening  a  string  have  on  the  pitch 
of  the  sound  it  gives  forth?  Does  a  coarse  or  a  fine 
string  have  a  lower  tone?  Why? 

Other  facts  about  sound.  Bodies  which  vibrate 
violently  and  send  large  air  waves  against  the  ear  give 
loud  sounds.  Bodies  which  vibrate  gently  and  send 
out  small  waves  give  faint  sounds.  ,  When  the  waves 
come  in  regular  succession  after  each  other  the  sound  is 
musical  and  pleasing  to  our  ears ;  when  they  come  irreg- 
ularly they  give  a  harsh  effect  which  we  call  a  "  noise." 


Sound  241 

These  and  many  other  interesting  subjects  relating  to 
sound  which  we  cannot  take  up  at  this  time  you  will 
understand  when  you  study  physics  and  the  physiology 
of  the  ear.  In  the  meantime,  when  you  listen  to  a  band 
or  an  orchestra  you  will  know  that  each  instrument  is 
causing  its  sound  by  vibrating  back  and  forth  and  send- 
ing out  waves  into  the  air ;  you  can  think  of  the  long  line 
of  little  molecules,  each  of  which  takes  up  the  motion  as 
the  sound  comes  to  you ;  and  your  curiosity  will  surely  be 
aroused  about  that  wonderful  instrument,  the  ear,  which 
receives  this  great  stream  of  air  vibrations  and  passes 
it  on  as  music  to  your  brain.  It  would  also  be  well  for 
you  to  remember  that  we  have  found  invisible  vibratory 
motion  where  we  were  not  looking  for  it,  and  that  we 
may  find  it  again  in  an  unexpected  place. 


CHAPTER  TWENTY-FIVE 


HEAT 

Go  out  of  doors  and  feel  the  wind  blowing  in  your  face. 

Why  does  not  the  great  covering  of  gas  which  we  call  the 

air  lie  quietly  on  the  surface 
of  the  earth?  Why  do  vast 
sheets  of  it  rush  hither  and 
thither,  sometimes  as  great 
storms  that  lash  the  sea  to 
fury  and  spread  destruction 
on  the  land?  Why  also  do 
the  waters  of  the  ocean  flow 
in  great  currents  over  their 
beds,  carrying  the  warmth  of 
the  tropical  seas  to  colder 
climes  and  the  coldness  of  the 
polar  oceans  to  the  heated 
regions  of  the  earth? 

Hold  your  hand  above  the 
register  of  a  hot-air  furnace. 
Why  does  the  heated  air  pour 
upward  through  the  pipes? 
Lay  your  hand  on  a  hot- water 
radiator.  Why  does  warm 
water  rise  into  the  radiator  and 
after  it  has  cooled  pass  down 
into  the  boiler  again?  Here 
is  motion  for  us  to  explain. 
Let  us  investigate  the  causes 

FIG.   147.   When  the  water  is  of    these    phenomena*    that 

heated   it  expands  and  is  forced  .  .    ,  11 

upward  into  the  tube.  are  so  important  to  us  all. 

242 


Heat 


243 


Exercise  i.  Repeat  the  experiment  described  on  page 
207.  Add  a  little  red  ink  to  the  water.  Allow  the  flask  to 
cool.  What  happens? 

Can  you  explain  your  experiment?  Think  it  through 
and  you  will  see  that  heating  the  air  caused  it  to  expand 
and  part  of  it  was  forced  out  of  the  flask.  When  the 
air  is  cooled  it  occupies  less  space,  and  the  water  is 
drawn  up  into  the  flask. 

Exercise  2.  Arrange  a  flask  as  shown  in  Figure  147. 
Fill  it  full  of  water  and  stopper  it,  so  that  the  water  rises 
part  way  into  the  tube.  Now  heat  the  water.  What  results 
do  you  get? 

Are  there  any  more  molecules  in  the  flask  of  water 
after  it  is  heated  than  before  ?  Does  it  weigh  any  more  ? 
Would  a  given  volume  of  warm  water  be  lighter  than  the 
same  volume  of  cold  water?  Would  a  given  volume  of 
warm  air  have  fewer  molecules  in  it  than  an  equal  volume 
of  cold  air  ?  Would  this  make  warm  air  lighter  than  cold 
air? 

Exercise  3.  Take  a, piece  of  stiff  paper  4  inches  square 
and  draw  the  diagonals.  From  the  corners  of  the  square 
cut  the  paper  along  these  diagonals  to  within  a  half  inch  of 
the  center  of  the  square.  From  the  corners  fold  each  alter- 
nate paper  point  over  to  the 
middle  and  bind  them  to  the 
middle  point  by  a  pin. 
Thrust  the  pin  through  the 
paper  into  a  stick  or  a  lead 
pencil. 

Now  hold  this  paper  wind- 
mill over  a  hot  stove,  handle  FIG.  148. 


244 


Science  for  Beginners 


FIG.  149.    Explain  why    there  are 
currents  in  the  water. 


up.  Do  you  find  a  rising 
column  of  air?  Explain  why 
the  air  rises  from  the  stove. 

Is  the  air  near  the  ceiling 
warmer  than  the  air  near 
the  floor  ?  Get  your  answer 
by  testing  with  a  thermom- 
eter. With  your  windmill 
or  a  piece  of  smoke  paper 
(page  30)  test  for  currents  of 
air  moving  in  various  direc- 
tions about  the  stove. 

Exercise  4.  Put  some  fine 
sawdust  or,  better,  a  bit  of 
blue  litmus  into  a  beaker  glass  of  water.  Gradually  heat  the 
water  and  notice  the  currents  in  the  water  as  indicated  by 
the  movement  of  the  dust  particles  (Fig.  149).  Does  the 
warm  water  rise  of  its  own  accord?  Or,  rather,  does  not 
the  cold,  and  therefore  heavier,  water  settle  to  the  bot- 
tom and  force  upward  the  warmer  and  lighter  water?  If 
this  is  the  case,  what  force  causes  heated  air  and  heated 
water  to  rise?  Explain  what  causes  the  movements  in  the 
water. 

Exercise  5.  Set  up  a  piece  of  apparatus  like  that  shown 
in  Figure  150  to  represent  a  hot- water  heating  system.  The 
flask  A  corresponds  to  the  furnace,  B  and  C  to  the  pipes 
and  radiator  of  the  heating  system,  and  D  to  the  expansion 
tank,  which  is  usually  placed  in  the  attic  or  upper  part  of 
the  house.  To  show  the  currents  add  litmus  or  other  colored 
liquid  to  C. 

Exercise  6.    Examine  a  hot- water  heating  system.    Trace 


Heat 


245 


the  pipes  through  the  house,  and 
explain  the  course  that  the  water 
takes.  Why  is  an  expansion  tank 
necessary  ? 

Some  questions  about  heat. 
We  have  now  learned  that  heat 
expands  air  and  water,  but  we 
have  still  to  ask  what  heat  is 
and  why  the  air  and  water 
expand  when  they  are  warmed. 
To  answer  these  questions  we 
must  return  to  the  subject  of 
vibratory  motion,  which,  in 
nature,  we  meet  again  and 
again.  We  will  repeat  an  ex- 
periment made  at  another  time 
and  for  another  purpose. 

Exercise  7.  Take  a  piece  of 
iron,  place  one  end  of  it  on  an 
anvil  or  solid  stone,  and  hammer 
it  vigorously.  It  becomes  warm; 
heat  is  produced  in  the  iron.  Ham- 
mer it  still  more,  using  greater 
force.  It  develops  greater  heat 
and  will  soon  become  uncom- 
fortably warm.  The  greater  the  pounding,  the  greater  the 
heat. 

What  heat  is.  What  change  does  the  pounding  make 
in  the  iron?  That  is,  what  is  heat?  Scientists  tell  us 
that  the  molecules  of  all  substances  are  always  in  motion 


FIG.  150.     Apparatus  illustrat- 
ing a  hot-water  heating  system. 


246 


Science  for  Beginners 


ATTIC 


EXE 

TO  KEEP  SYSTEM 
FULL. :  SUPPLIES  FROM 
WATER  CIRCULATION 
OF  HOUSE 


OVERFLOW  TO 
GUTTER.  FROM 
EXPANSION  TAW 


RETURN  TO 
BOILER 


CELLAR. 


FIG.  151.     Diagram  of  a  hot-water  heating  system. 

to  and  fro ;  that  they  constantly  dance  back  and  forth 
with  a  vibratory  motion.  When  the  movement  of  the 
molecules  is  slight,  the  substance  is  cold.  When  the 
molecules  move  very  rapidly,  the  substance  is  hot. 
Heat,  then,  may  be  thought  of  as  the  motion  of  the 
molecules,  and  when  we  pound  the  iron  we  jar  the 
molecules  and  set  them  to  vibrating  more  rapidly. 

Heat  is  easily  recognized  by  the  sensation  of  warmth 
which  it  gives  to  the  touch.  That  is,  when  we  touch  any- 
thing and  feel  the  molecules  pounding  with  great  vigor 
against  our  hand,  we  say  it  is  hot.  If  heat  is  the  motion 
of  the  molecules,  what  is  cold? 

Why  heated  substances  expand.  Can  your  own 
imagination  now  tell  you  why  heated  substances  expand  ? 
Suppose  the  molecules  of  the  iron  are  set  to  vibrating 
more  vigorously,  will  they  not  drive  each  other  farther 
apart  ?  Think  over  this  matter,  and  when  you  lay  your 


Heat 


247 


finger  on  the  bulb  of  a  thermometer  and  see  the  mercury 
rise  in  the  tube,  picture  in  your  mind  how  you  are 
quickening  the  millions  of 
little  molecules  in  their 
dance. 

Conduction  of  heat.  When 
heated  air  or  heated  water 
moves  from  one  place  to 
another,  it  of  course  carries 
with  it  the  heat  it  contains. 
This  method  of  transporting 
heat  is  called  convection. 
We  speak  of  convection 
currents  in  the  water  and 
the  air.  Heat  is  transmitted 
in  another  way  also,  which 
we  can  illustrate  by  an  ex- 
periment. 

Exercise  8.  Hold  one  end  of  an  iron  poker  in  the  fire. 
The  heat  is  transferred  from  one  end  of  the  poker  to  the  other. 
Explain  what  you  think  the  molecules  are  doing  as  the 
heat  travels  along  the  poker. 

Exercise  9.  Take  a  piece  of  iron  wire  two  or  three  inches 
long;  fasten  one  end  to  the  head  of  a  match,  andliold  the 
other  in  the  flame  of  a  candle  or  a  lamp.  What  are  the 
results  ? 

In  the  above  experiments  the  heat  travels  by  con- 
duction through  the  iron.  The  motion  passes  from 
molecule  to  molecule  as  motion  passes  from  block  to 
block  in  a  row  that  has  been  set  up  and  knocked  down 


FIG.  152.    One  rod  is  a  better  con- 
ductor of  heat  than  the  other. 


248  Science  for  Beginners 

by  a  child.  Heat  travels  by  conduction  through  liquids 
and  gases  as  well  as  through  solids,  but  in  liquids  and 
gases  the  molecules  are  free  to  leave  their  places  and 
travel  about,  and,  as  we  have  learned,  heat  may  be  trans- 
ported by  convection  also. 

Exercise  10.  Arrange  a  glass  rod  and  a  metal  rod,  or  a 
copper  rod  and  an  iron  rod,  as  shown  in  Figure  152.  Now, 
with  drops  of  wax,  fasten  small  marbles  or  large  shot  along  the 
rods  at  equal  intervals.  With  an  alcohol  lamp  or  a  Bunsen 
burner  heat  the  ends  of  the  rods  equally.  What  results  do 
you  get? 

Do  all  bodies  conduct  heat  alike?  What  is  the 
philosophy  of  the  cloth  "  holder  "  commonly  used  with 
hot  dishes  ?  Is  a  wooden  handle  or  an  iron  handle  better 
for  use  on  a  hot  iron  ?  Why  are  boilers  and  steam  pipes 
wrapped  with  asbestos?  What  kind  of  clothing  should 
we  wear  in  cold  weather  ?  in  warm  weather  ?  With  what 
would  you  wrap  a  water  pipe  to  protect  it  during  very 
cold  weather?  What  is  between  the  two  layers  of  a 
thermos  bottle  ?  Why  should  this  be  an  excellent  pro- 
tection from  heat  or  cold? 

Exercise  n.  Place  your  bare  hand  or  foot  upon  the  oil- 
cloth and  then  upon  the  carpet  next  to  it.  Which  is  the 
warmer  ?  Test  with  the  thermometer  and  see  how  mistaken 
you  are. 

Why  does  the  oilcloth  seem  colder  than  the  carpet? 
Why  does  -a  marble-top  table  seem  colder  than  a  wooden 
table  hi  the  same  room?  The  oilcloth  and  the  marble 
are  better  conductors  of  heat  than  the  carpet  and  the 
wood.  They  therefore  conduct  more  heat  away  from  the 


Heat 


249 


hand  or  foot  and  for  this 
reason  feel  colder.  Iron 
conducts  heat  about  100 
times  as  well  as  water 
and  about  2500  times 
better  than  air.  Find 
out  what  materials  are 
in  the  walls  of  an  ice 
box.  Why  does  a  fire- 
less  cooker  hold  heat  ? 
Radiant  heat.  Heat 


Heat  is  given  off  by  radiation 
from  the  iron. 


FIG.  153. 

comes  to  us  from  the  sun. 

It  travels  across  space  in  which  there  is  no  air  through 

which  it  can  be  carried  by  convection  or  conduction. 

Exercise  12.  Suspend  a  piece  of  iron  by  a  wire  and 
heat  it  with  a  gas  burner.  A  common  flatiron  heated  and 
then  held  as  is  shown  in  Figure  153  may  be  used  in  this 
experiment.  Hold  the  hand  beneath  the  iron.  The  air  is 
rising  and  the  heat  will  not  reach  the  hand  by  convection  or 
conduction ;  yet  a  sensation  of  warmth  is  felt  by  the  hand. 

The  heat  is  given  off  by  radiation  from  the  iron  and  is 
called  radiant  heat.  The  explanation  of  how  it  comes  to 
the  hand  will  be  deferred  until  a  later  chapter  (page  336). 

Sources  of  heat.  We  may  discover  some  of  the  sources 
of  heat  for  ourselves. 

Exercise  13.  Find  out  how  the  Indian  produced  fire. 
Repeat  his  experiment  in  some  form.  At  least,  brush  your 
dry  hand  briskly  over  your  coat  sleeve,  rub  a  piece  of  metal 
upon  a  smooth  board,  or  draw  a  nail  from  a  hard  board  and 
note  that  heat  is  produced  by  friction. 


25° 


Science  for  Beginners 


FIG.  154. 


In  connection  with  these  experiments  review  Exer- 
cise 7.  Then  you  may  be  prepared  to  believe  that 

whenever  motion  is  checked, 
heat  is  produced.  Motion 
is,  therefore,  a  source  of  heat. 
What  causes  a  meteor  to 
become  hot  when  it  falls 
through  the  air? 

Exercise  14.  S trike  a  match 
and  answer  one  or  two  ques- 
tions, (a)  How  much  heat  was 
produced  by  the  friction? 
The  answer  is,  enough  to  raise 
the  chemicals  on  the  match  to 
the  kindling  point.  (£>)  What  happens  next?  The  oxygen 
of  the  air  is  now  able  to  unite  with  the  chemicals  of  the  match 
head  to  produce  more  heat. 

Why  do  we  open  the  draught  of  the  stove  or  furnace 
when  the  fire  burns  low?  Note  the  heat  produced  as 
the  mason  puts  water  on  the  lime  in  the  process  of  making 
mortar.  Perhaps  you  can  make  this  experiment  for 
yourself. 

Another  and  very  common  source  of  heat  is  chemical 
action.  Great  supplies  of  heat  that  can  be  released 
in  this  way  are  found  in  our  stores  of  wood  and  coal. 
From  what  source  does  the  heat  come  that  warms  your 
own  body? 

Exercise  15.  Introduce  a  small,  thin  iron  wire  into  the 
circuit  of  an  electrical  battery.  The  wire  is  a  poor  conductor 
of  electricity  and  for  this  reason  the  flow  of  the  electricity  is 


Heat 


251 


FIG.  155.    Our  greatest,  and  in  the  end  our 
only,  source  of  heat  is  the  sun. 


obstructed,  the  result  be- 
ing that  heat  is  produced. 

This  experiment  shows 
that  a  third  source  of 
heat  is  electricity.  The 
incandescent  filament  of 
an  electric  lamp  is  a 
familiar  example  of  a 
body  heated  by  elec- 
tricity. 

Exercise  16.  Step  from  the  shade  into  the  bright  sun- 
shine. What  change  in  temperature  do  you  note? 

Secure  a  reading  glass  and  concentrate  the  rays  of  the 
sun  in  a  fine  point  on  a  piece  of  cloth  or  paper.  Hold  the 
glass  steady  for  some  time.  What  happens? 

A  fourth  source  of  heat  is  the  sun.  It  warms  the 
whole  earth  and  the  other  members  of  the  solar  system, 
and  in  the  end  it  is  our  only  source  of  heat,  for  it 
is  the  sunshine  that  enables  plants  to  build  the  food 
that  warms  our  bodies  and  the  wood  and  coal  that 
heat  our  homes.  The  sun  also  gives  us  our  water 
power  by  lifting  the  water  of  streams  to  the  moun- 
tain tops,  and  the  heat  of  the  sun  causes  the  great  cur- 
rents of  air  that  turn  our  windmills  and  drive  our  ships 
across  the  seas.  Silently  as  the  grass  covers  the  hillsides 
in  the  spring  the  heat  of  the  sun  leaps  through  ninety 
millions  of  miles  of  space  to  us ;  but  without  this  mighty 
force  all  life  and  motion  in  the  world  would  soon  be 
stilled,  and  our  earth  would  be  but  a  frozen  ball  swinging 
onward  through  space. 


CHAPTER  TWENTY-SIX 

HOW  TO   MEASURE   TEMPERATURES 

Do  you  already  know  that  heat  and  cold  do  not  mean 
two  different  things?  Heat  and  cold  are  relative  terms 
used  to  show  whether  a  body  or  a  substance  has  more  or 
less  of  heat.  In  common  speech  we  say  of  anything 
which  is  warmer  than  our  body  that  it  is  warm;  if  it 
has  a  lower  temperature  than  our  body  we  say  it  is  cold. 
In  both  cases,  however,  there  is  motion  among  the  mole- 
cules. The  difference  is  that  they  move  faster  in  the 
warmer  body  and  more  slowly  in  the  colder  body. 

Measuring  temperature.  How  shall  we  measure 
temperature?  Within  certain  limits  the  nerves  in  our 
skin  enable  us  to  do  this.  Let  us  see  how  accurate 
they  are. 

Exercise  i.  Provide  three  dishes  of  water,  with  the  water 
in  the  first  as  hot  as  the  hand  will  endure  without  scalding ; 
the  second  filled  with  water  which  has  just  come  from  the 
well  or  hydrant ;  and  a  third  containing  ice  water. 

(1)  Place  the  hand  in  the  first  dish  for  a  moment  or  two 
and  then  in  the  second.     The  latter  will  feel  cold. 

(2)  Place  the  other  hand  for  a  moment  in  the  third  dish 
and  then  transfer  it  to  the  second.    The  latter  will  now  feel 
quite  warm. 

Exercise  2.  Put  your  hand  into  water  which  has  been 
standing  in  the  room  for  some  time.  Which  is  warmer,  the 
air  or  the  water?  After  you  have  judged  the  case  with  your 
hand,  try  it  with  the  thermometer.  Both  air  and  water 
will  be  found  to  be  of  the  same  temperature. 

It  seems,  then,  that  while  the  nerves  of  the  skin  can 
be  used  in  a  general  way  to  tell  temperatures,  they 

252 


How  to  Measure  Temperatures 


253 


cannot  be  depended  upon  for 
great  accuracy.  They  can  only 
compare  two  or  more  bodies 
which  are  so  near  together  that 
they  may  be  tested  at  the  same 
time;  and  they  cannot  compare 
two  substances  of  different  kinds. 
We  see,  therefore,  that  we  need 
a  more  accurate  instrument  for 
measuring  temperatures,  and  for 
this  purpose  we  have  the  ther- 
mometer.* 

The  thermometer.  Every  home 
and  schoolroom  should  have  at 
least  one  fairly  good  thermometer. 
One  can  be  purchased  for  from 
twenty-five  cents  to  a  dollar. 

Exercise  3.  Study  the  construc- 
tion of  the  thermometer.  Note  the 
tube  closed  at  both  ends,  the  bulb, 
and  the  graduation.  It  will  be  more 
convenient  for  many  purposes  if 
the  thermometer  is  not  fixed  to  a 
board  or  frame  of  iron.  Hold  the  bulb  in  "your  hand  for  a 
minute.  The  mercury  rises.  Explain  why.  Finally  it  comes 
to  a  point  beyond  which  it  does  not  go.  Why  does  it  stop 
at  this  point? 

The  Fahrenheit  and  centigrade  scales.  The  ther- 
mometers used  in  different  countries  are  exactly  alike 
in  the  construction  of  the  tube  but  differ  in  the  way 


FIG.  156. 


254 


Science  for  Beginners 


—100* 


212'- 


194* 


176* 


they   are   marked.      The   two   scales   most   commonly 

employed  are  the  Fahrenheit  and  centigrade.* 

Exercise  4.  Test  the  graduation  of 
your  thermometer,  as  follows  :  Place 
several  coarse  pieces  of  ice  in  a  dish  con- 
taining pure  water  and  allow  it  to  stand 
for  a  few  minutes.  Stir  the  ice  in  the 
water  thoroughly  to  make  the  temper- 
ature the  same  in  all  its  parts.  Now 
place  the  thermometer  in  the  water  and 
note  the  temperature.  If  you  are  using 
a  centigrade  thermometer,  the  tem- 
perature should  be  at  zero.  If  you  are 
using,  a  Fahrenheit  thermometer,  the 
temperature  should  be  32  degrees. 

Add  more  ice  and  note  the  tempera- 
ture. See  whether  the  temperature 
differs  when  the  bulb  of  the  thermome- 
ter is  against  the  ice  and  when  it  is 
merely  in  the  water.  Very  gradually 
heat  the  water,  constantly  stirring  the 
ice  and  testing  with  the  thermometer. 
What  is  the  freezing  point  of  water? 
What  is  the  melting  point  of  ice  ? 

It  requires  nearly  four  fifths  as 
much  heat  to  melt  a  pound  of  ice  as 
it  does  to  raise  from  the  freezing  to 
the  boiling  point  the  water  that 
comes  from  the  ice.  During  the 

melting  process  the  temperature  is  not  raised  at  all. 

The  heat  is  used  in  changing  the  water  from  the  solid 


-17.78°  HH 


FIG.  157.  Comparison 
of  the  centigrade  and 
Fahrenheit  thermom- 
eters. 


How  to  Measure  Temperatures 


255 


to  the  liquid  state. 
When  we  buy  a  block 
of  ice,  therefore,  we 
are  buying  something 
that  has  a  great  ca- 
pacity to  absorb  heat. 

Exercise  5.  Partly 
fill  with  water  a  flask 
(Fig.  1 60)  provided  with 
two  openings.  An  ordi- 
nary teakettle  may  be 
used.  In  one  opening 
place  a  thermometer. 
Bring  the  water  to  the 
boiling  point  and  note 
the  temperature  of  the 
steam  and  also  of 
the  water.  Continue 
the  boiling  for  several 
minutes,  placing  the 
bulb  of  the  thermometer 
alternately  in  the  steam 
and  in  the  water. 

Does  the  thermome- 
ter show  a  higher  temperature  if  the  heat  has  been  applied 
to  the  water  for  several  minutes  after  it  has  begun  to  boil  ? 
The  mercury  remains  at  a  fixed  point  as  long  as  the  water 
continues  to  boil.  What  is  the  boiling  point  of  water?  At 
what  temperature  will  water  vapor  begin  to  condense? 

We  have  now  determined  two  points  on  our  ther- 
mometer :  the  freezing  and  the  boiling  point  of  water. 


FIG.  158.  The  melting  of  the  ice  absorbs 
heat,  and  the  temperature  of  the  water  does 
not  rise  until  all  the  ice  has  disappeared. 


256 


Science  for  Beginners 


Figure  157  shows  the  fixed  points  on  the  centigrade  (C.) 
and  the  Fahrenheit  (F.)  thermometers.  Notice  that  the 
difference  between  the  freezing 
and  the  boiling  point  of  water  is 
divided  into  100  degrees  on  the 
centigrade  thermometer  and  into 
1  80  degrees  on  the  Fahrenheit 
thermometer,  and  that  therefore 
100  degrees  C.  equals  180  de- 
grees F. 

Freezing  mixtures.  The  Fah- 
renheit thermometer  has  a  point 
marked  o  which  is  32  degrees 
below  the  freezing  point  of  water. 
When  we  wish  to  freeze  ice  cream 
we  sprinkle  salt  liberally  over  the 
ice  which  is  around  the  freezer. 
How  does  salt  help  to  freeze  ice 
cream  ? 

Exercise  6.  Take  two  dishes  of 
snow  or  ice  and  test  the  tempera- 
tures. Stir  a  considerable  quantity 
of  salt  into  one  dish.  Again  test 
the  temperatures.  Consider  the 
following  questions  : 

(1)  Does  the  salt  cause  the  snow 
or  ice  to  dissolve  more  rapidly  ? 

(2)  What  is  required  in  Border 
that  a  solid  may  be  changed  into  a 
Kq»M?     Review  the  first  part  of 

the  boiling  point.  Exercise  4. 


FIG.XSO.  The  evaporation  of 
the  water  takes  up  heat,  and 


How  to  Measure  Temperatures  257 

(3)  If  heat  is  required,  must  the  object  which  furnishes 
the  heat  become  colder? 

(4)  Does  salt  water  freeze  at  a  lower  temperature  than 
water  that  contains  no  salt? 

Exercise  7.  Place  a  small,  tightly  corked  vial  of  sweetened 
cream  (water  may  be  used  for  a  "  make  believe  "  sweetened 
cream)  in  the  midst  of  the  dissolving  ice  and  salt.  What 
happens?  What  would  you  have  if  you  should  do  this  on 
a  large  scale  ?  If  you  should  find  the  vial  broken,  how  would 
you  explain  the  circumstance? 

Can  you  now  explain  clearly  why  salt  is  used  in  freezing 
ice  cream? 

In  the  year  1714  a  German  named  Fahrenheit  in- 
vented the  thermometer  which  bears  his  name.  He 
packed  it  in  a  mixture  of  chemical  salts  and  snow  and 
marked  as  zero  the  lowest  point  of  the  mercury  that 
he  could  obtain  in  this  way.  In  1742  the  centigrade 
thermometer  was  invented  by  Celsius,  a  Swede. 

Heat  required  to  evaporate  liquids.  Review  the 
second  part  of  Exercise  4.  It  requires  almost  5^  times 
as  much  heat  to  turn  boiling  water  into  steam  as  is 
needed  to  raise  the  same  amount  of  water  from  the  freez- 
ing to  the  boiling  point.  By  experiment  you  can  prove 
that  heat  is  required  to  change  a  liquid  into  a  gas. 

Exercise  8.  Moisten  your  hand  with  ether,  alcohol, 
or  gasoline.  As  the  liquid  turns  into  a  gas,  the  hand  feels 
cold.  The  hand  is  robbed  of  a  large  amount  of  heat  to 
produce  the  gas. 

Exercise  9.  Place  a  drop  or  two  of  water  upon  a  board 
and  set  on  the  water  a  watch  glass  containing  a  small 
quantity  of  ether.  Now  cause  the  ether  to  evaporate 


258  Science  for  Beginners 


rapidly  by  blowing  a  current 
of  air  across  it.  The  watch 
glass  will  be  frozen  to  the 
board. 

What  is  the  effect  pro- 
duced by  perspiration  on 
a  hot  day?  Why  do  we 


takes  up  heat  and  freezes  the  watch     heat      Ul     humid      Slimmer 

glass  to  the  board.  weather? 

Ice  making.  In  an  ice  plant  ammonia  gas  is  drawn 
into  a  pump  and  put  under  great  pressure.  In  this 
way  it  is  converted  into  a  liquid.  The  liquid  ammonia 
is  then  allowed  to  escape  as  a  gas  through  coils  of  pipes 
that  run  through  a  tank  of  brine  (B)  .  The  evaporation 
of  the  ammonia  takes  up  heat  and  makes  the  pipes  and 
the  brine  very  cold.  The  ammonia  gas  is  then  again 
sucked  from  the  pipes  by  the  pumps,  reduced  to  a  liquid, 
and  once  more  allowed  to  escape  as  a  gas,  and  so  the 
process  is  continued. 

The  brine  about  the  pipes  containing  the  ammonia 
does  not  freeze,  because  of  the  salt  that  is  in  it  (page  257), 
and  a  second  pump  causes  it  to  circulate  through  a 
larger  tank  (C)  .  The  ice  is  produced  by  lowering  deep, 
flat-sided  iron  vessels  (D)  filled  with  distilled  water 
into  this  tank  until  the  water  is  frozen.  The  blocks  of 
ice  are  loosened  from  the  walls  of  the  vessels  in  which 
they  are  frozen  by  dipping  the  vessels  in  hot  water.  In 
cold-storage  plants  the  pipes  containing  the  cold  brine 
run  through  the  rooms  that  are  to  be  chilled.  When 


How  to  Measure  Temperatures 


259 


FIG.  161.    Plan  of  an  ice-making  machine.     (Diagrammatic.) 

the  gaseous  ammonia  is  condensed  heat  is  given  off, 
and  it  is  necessary  to  keep  cold  water  flowing  about  the 
pipes  in  which  the  liquid  ammonia  is  contained. 

Exercise  10.  Visit  an  ice  factory  or  a  refrigerating  plant 
and  learn  how  the  low  temperature  is  produced. 

Temperature  and  quantity  of  heat.  We  must  re- 
member that  the  thermometer  is  only  useful  to  measure 
the  intensity  of  heat  —  how  hot  a  body  is  —  and  cannot 
be  used  directly  to  measure  the  quantity  of  heat.  A 
comparatively  small  amount  of  heat  will  raise  the  tem- 
perature of  a  fine  platinum  wire  to  a  temperature  of 
1600  degrees.  The  quantity  of  heat  in  this  case  is  very 
small,  though  the  temperature  is  very  high.  It  is  there- 
fore important  that  we  should  keep  clearly  in  mind 
the  difference  between  temperature  and  quantity  of  heat. 
Temperature  depends  upon  the  rapidity  of  the  vibration 
of  the  molecules,  and  this  is  measured  in  degrees  by  a 
thermometer.  The  amount  of  heat  which  a  body  con- 
tains depends  upon  the  weight  and  the  material  of  which 
it  is  composed,  as  well  as  upon  its  temperature. 

If  we  should  take  a  cupful  of  water  from  a  lake  and 


260  Science  for  Beginners 

test  with  the  thermometer  both  the  water  in  the  lake 
and  the  water  in  the  cup,  the  temperature  of  the  water 
in  the  two  cases  would  be  the  same.  On  the  other 
hand,  it  is  evident  that  the  total  quantity  of  heat  in 
the  cup  would  be  only  a  small  fraction  of  the  total 
amount  of  heat  in  the  lake.  What  would  be  the  tem- 
perature if  we  should  take  2  cupfuls  from  the  lake? 
What  quantity  of  heat  would  be  in  2  cupfuls  as  com- 
pared with  the  heat  in  i  cupful?  Three  cupfuls  would 
have  the  same  temperature  as  i  cupful,  but  3  times 
as  much  heat.  The  quantity  of  heat  depends  upon  the 
amount  of  water  taken. 

Exercise  i-i.  Fill  a  pint  and  a  quart  cup  from  the  same 
source  of  hot  water.  Take  the  temperature  with  the  ther- 
mometer in  each  case.  What  is  the  temperature  and  what  is 
the  quantity  of  heat  in  each  case  ? 

Exercise  12.  Take  a  measured  amount  of  water,  find 
its  temperature,  and  mix  it  with  an  equal  amount  of  boil- 
ing water.  When  the  hot  and  cold  water  are  thoroughly 
mixed,  take  the  temperature  of  the  mixture. 

To  measure  the  quantity  of  heat.  Heat,  like  every 
other  useful  thing,  is  bought  and  sold,  and  therefore  it 
must  be  accurately  measured.  Liquids  are  measured  by 
the  quart  or  the  liter ;  solids,  by  the  pound  or  kilogram. 
Heat  may  be  measured  by  the  use  of  one  or  the  other  of 
two  units :  (i)  the  British  thermal*  unit,  based  on  the 
pound  weight  and  the  Fahrenheit  degree,  and  (2)  the 
calorie,  based  on  the  gram  weight  and  the  centigrade 
degree. 


How  to  Measure  Temperatures  261 

A  British  thermal  unit  (B.T.U.)  is  the  quantity  of  heat 
required  to  raise  one  pound  of  water  one  degree  Fahren- 
heit.  Weigh  out  a  pound  of  water  and  examine  the 
degrees  marked  on  a  Fahrenheit  thermometer.  Have 
you  a  clear  idea  of  what  a  British  thermal  unit  is? 

Exercise  13.  Weigh  out  a  certain  quantity  of  water, 
say  2  pounds.  Take  the  temperature  with  the  Fahrenheit 
thermometer.  Place  the  water  on  a  stove  or  a  hot  radiator, 
or  apply  a  flame  to  it  for  some  time.  Before  the  water  boils, 
remove  it  from  the  stove  or  radiator,  stir  it  thoroughly, 
and  note  the  temperature. 

If  the  original  temperature  was  60  degrees  and  the  final 
temperature  is  130  degrees,  then  2  pounds  of  water  have 
been  raised  70  degrees,  and  the  amount  of  heat  absorbed  by 
the  water,  as  the  result  of  heating,  is  2  x  70  =  140  British 
thermal  units  (B.T.U. 's). 

Coal  is  usually  bought  at  a  fixed  price  by  the  ton.  The 
power  of  coal  to  produce  heat  varies  greatly,  and  since 
it  is  the  heat  we  want,  it  would  be  more  scientific  if  we 
had  our  coal  tested  so  that  we  could  know  accurately  how 
many  British  thermal  units  a  ton  would  produce.  This 
is  done  by  many  manufacturing  companies  that  use  a 
large  amount  of  coal.  The  amount  of  heat  in  coal  is  de- 
termined by  finding  how  much  a  pound  of  the  coal  raises 
the  temperature  of  a  given  number  of  pounds  of  water. 

A  calorie  is  the  quantity  of  heat  which  is  required  to 
raise  i  gram  of  water  i  degree  centigrade.1  A  gram 

1  In  tables  showing  the  heat  values  of  foods  for  men  and  animals 
the  large  Calorie  (written  with  a  capital  C)  is  the  unit  used.  This  is 
the  amount  of  heat  required  to  raise  the  temperature  of  i  liter  of  water 
i  degree  centigrade.  It  is  equal  to  1000  calories  as  defined  above. 


262 


Science  for  Beginners 


of  water  is  a  cubic  centimeter.  Measure  or  weigh  it  out 
and  see  how  much  it  is.  Examine  the  degrees  on  a  centi- 
grade thermometer. 
Is  a  British  thermal 
unit  or  a  calorie  the 
larger  unit? 

Exercise  14.  Weigh 
out  a  certain  quan- 
tity of  water,  say  750 
grams.  Take  the 
temperature  with  the 
centigrade  thermom- 
eter. Heat  it  for  a 
time.  Remove  the 
source  of  heat,  mix 
the  water  thoroughly 
by  stirring  with  the 
thermometer,  and 
again  take  the  tem- 
perature. • 

If  the  difference 
between  the  two 
temperatures  was  58 
degrees,  the  amount 
of  heat  absorbed  by 
the  750  grams  of 
water  would  be  750  X 
58  =  43,500  calories. 
Exercise  15.  Weigh 
a  certain  amount  of 
hot  water,  using 
either  the  pound  or 


FIG.  162.  Exact  size  of  measures  that  hold  i 
cubic  centimeter  and  10  cubic  centimeters. 
What  is  a  calorie? 


How  to  Measure  Temperatures  263 

the  gram  weights.  Take  the  temperature.  Allow  it  to  stand 
for  some  time  and  take  the  temperature  again.  How  many 
heat  units  has  it  lost  during  that  time? 

Exercise  16.  Place  a  pail  on  one  pan'  of  a  balance  and 
enough  weights  on  the  other  pan  to  balance  it.  Place  a  flat- 
iron  on  the  pan  with  the  weights  and  pour  enough  water  into 
the  pail  to  balance  the  iron.  Now  place  the  iron  in  the  pail 
with  the  water.  Set  the  pail  and  its  contents  on  the  stove 
in  a  place  that  is  warm,  but  not  hot  enough  to  bring  the 
water  to  the  boiling  point.  Let  the  pail. stay  on  the  stove 
until  the  iron  is  warmed  in  all  its  parts  and  the  iron  and 
water  are  thus  brought  to  the  same  temperature. 

Provide  two  vessels,  with  the  same  weight  of  cold  water, 
at  the  same  temperature,  in  each.  Take  the  temperature. 
Set  the  flatiron  in  one  of  the  vessels  of  cold  water  and  pour 
the  water  from  the  pail  into  the  other.  At  the  end  of  a  cer- 
tain time,  —  for  instance,  three  minutes,  —  take  the  tem- 
perature of  the  water  in  both  vessels.  The  water  should  be 
thoroughly  stirred  in  both  cases,  before  taking  the  tempera- 
ture. 

Different  substances  have  different  heat-holding  ca- 
pacities. You  are  now  ready  to  answer  some  interesting 
questions  and  to  make  a  very  practical  application  of  the 
knowledge  gained  in  the  last  exercise.  Which  of  the  two 
samples  of  cold  water  gained  the  more  heat  during  the 
three  minutes  of  time?  Which  contained  more  heat, 
the  hot  iron  or  the  equal  weight  of  hot  water?  When 
you  go  sleigh  riding,  which  would  be  better  to  place 
under  your  feet  as  a  foot  warmer,  a  hot  flatiron,  wrapped 
in  a  woolen  cloth,  or  an  equal  weight  of  water  at  the 
same  temperature  in  a  hot- water  bag  ? 


264  Science  fot  Beginners 

A  given  weight  of  water  holds  more  heat  than  an 
equal  weight  of  any  other  common  substance  at  the  same 
temperature.  Pound  for  pound  it  contains  8  times  as 
much  heat  as  iron,  10  times  as  much  as  copper,  20  times 
as  much  as  tin  or  silver,  and  20  times  as  much  as  mercury. 
Give  two  reasons  why  in  temperate  climates  large  lakes 
make  the  climate  of  places  near  them  cooler  in  spring 
and  warmer  in  autumn. 


CHAPTER  TWENTY-SEVEN 

PRACTICAL  THERMOMETRICAL   PROBLEMS 


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FIG.  163.    Mean  daily  temperature  graph  at  Albion,  Michigan,  from 
December  6  to  December  24,  1914. 

Exercise  i.  Hang  a  thermometer  in  your  room  at  home. 
By  observation  and  experience  learn  what  is  meant  by 
"  ordinary  temperature,"  C.  degrees  and  F.  degrees,  of  the 
room  at  various  hours  of  the  day  and  night  and  for  several 
days.  Preserve  in  tabulated  form  the  results  of  your  obser- 
vations. 

Exercise  2.  At  the  schoolhouse  make  hourly  observations 
of  the  thermometer  readings  and  preserve  them  in  a  blank 
book  provided  for  the  purpose. 

Exercise  3.  At  the  end  of  each  week  compute  the  answer 
to  the  following  questions  and  record  the  results  in  a  note- 
book. What  is  the  mean,  or  average,*  hourly  temperature 
for  each  day  you  have  observed?  What  is  the  mean  daily 
temperature  for  the  days  you  have  observed?  Take  these 
reports  home  to  your  parents. 

Exercise  4.  Construct  a  graphic  chart  of  your  observa- 
tions similar  to  Figure  163.  Take  the  average  of  three 
observations  of  the  thermometer  at  7  A.M.,  2  P.M.,  and  9  P.M., 
as  the  mean  daily  temperature.  Make  a  mark  on  the  chart 
for  each  day,  showing  the  mean  daily  temperature  for  that 

265 


266  Science  for  Beginners 


FIG.  164.    Weather  records  kept  by  a  class  in  the  Jefferson  Street  School, 
Grand  Rapids,  Michigan. 

• 

day.  At  the  end  of  the  month  draw  a  curved  line  joining 
all  the  points.  The  chart  will  then  show  at  a  glance  the 
variations  in  temperature  for  the  entire  time.  The  curved 
line  is  called  a  thermograph*  or  temperature  graph. 

Be  sure  that  you  are  able  to  read  the  thermograph. 
From  Figure  163  determine  what  was  the  mean  tempera- 
ture for  December  12.  What  was  it  for  December  9? 
When  was  the  highest  temperature  reached  and  what  was 
the  mean  temperature  at  that  date?  When  did  the 
lowest  temperature  occur  ?  Notice  that  the  temperature 
must  have  been  considerably  lower  than  zero  at  some 
time  in  the  day  in  order  to  give  an  average  of  zero. 

A  more  instructive  temperature  graph  and  one  from 
which  many  valuable  lessons  may  be  learned  may  be 
constructed  from  readings  taken  hourly  for  a  week  or 
more.  It  requires  some  trouble  to  take  the  readings, 
especially  through  the  night,  but  three  or  four  of  the 


Practical  Thermometrical  Problems        267 

class    could    easily    organize    themselves    into    relays* 
and  thus  obtain  all  the  data  needed. 

When  the  graph  has  been  constructed,  it  can  be  placed 
upon  the  blackboard  and  various  facts  read  from  it : 

(1)  Study  the  daily  range  of  temperature. 

(2)  From  the  first  graph  construct  a  second,  showing 
the  average  temperature  for  the  hours  between  sunrise 
and  sunset,  and  another  for  the  hours  between  sunset 
and  sunrise.     Study  the  range  between  these  limits. 

(3)  From  the  original  graph,  note  the  hours  of  maxi- 
mum and  minimum  temperature. 

Study  the  chart  shown  in  Figure  164  until  you  can 
read  every  fact  on  it.  What  was  the  highest  temperature 
in  March  ?  in  May  ?  What  was  the  lowest  temperature 
in  each  of  the  months?  The  arrows  in  the  calendars 
show  the  direction  of  the  wind ;  the  one  at  the  top  of  a 
square  shows  the  direction  in  the  forenoon,  the  lower 
one  in  the  afternoon.  Prepare  a  similar  chart  for 
yourself. 

Exercise  5.  Let  several  persons  hold  a  thermometer 
in  the  hand  until  the  mercury  has  risen  as  far  as  it  will  go. 
After  each  test,  allow  the  thermometer  to  cool.  Tabulate 
the  tests  and  compare.  It  will  probably  be  found  that  the 
temperature  of  the  hands  of  the  different  persons  varies 
somewhat. 

Exercise  6.  Place  the  bulb  of  the  thermometer  in  your 
mouth  and  under  the  tongue,  holding  it  there  for  at  least  2 
minutes.  Note  the  temperature,  which  will  be  found  to  be 
about  98  degrees  F.,  provided  you  have  a  reliable  thermom- 
eter and  your  body  is  at  a  normal  temperature.  This  is 
the  method  by  which  the  doctor  learns  whether  you  have  a 


268  Science  for  Beginners 

higher   temperature,  —  or,   as   the   case   may  be,   a   lower 
temperature,  —  than  you  ought  to  have. 

Bacteria.  To  take  the  temperatures  of  a  number  of 
the  members  of  the  class  in  this  way,  the  pupils  will  need 
one  after  another  to  take  the  bulb  of  the  thermometer  into 
their  mouths.  Before  they  do  this,  however,  we  should 
pause  long  enough  to  study  some  facts  which  have  a 
very  great  and  practical  interest  at  this  point. 

The  sanitarian*  will  tell  you  that  there  is  a  large  num- 
ber of  bacteria  in  your  mouth  all  the  time,  whether  you 
are  well  or  ill.  Bacteria  are  very  low  forms  of  plant 
life,  —  tiny  sacs  or  cells,  as  they  are  properly  called. 
They  are  alive  and  are  composed  of  a  curious  jellylike 
substance  called  protoplasm.*  They  are  present  in 
large  numbers  in  earth  and  water,  and  when  they  gain 
access  to  liquids  which  contain  material  suitable  for 
their  growth,  they  multiply  with  great  rapidity,  so 
that  a  single  bacterium,  if  placed  in  milk  or  some 
other  suitable  food,  will  develop  into  many  millions  in 
the  course  of  one  hot  night.  Most  bacteria  are  harmless, 
and  many  of  them  are  useful,  but  some  of  them  grow  in 
our  bodies  and  cause  illness.  These  dangerous  kinds 
are  called  germs,  and  some  of  them  might  exist  in  the 
mouth  of  one  person  without  doing  him  any  apparent 
injury.  If,  however,  they  were  transferred  to  the  mouth 
of  another,  they  might  grow  and  produce  disease.* 

Exercise  7.  Place  some  white  of  egg  in  a  test  tube. 
Set  the  tube,  along  with  a  thermometer,  in  a  vessel  of  water 
and  gradually  heat  the  water.  At  what  temperature  does 
the  white  of  egg  coagulate*  or  harden? 


Practical  Thermometrical  Problems        269 

The  protoplasm  of  which  bacteria  are  made  is  very 
similar  to  the  white  of  the  egg,  and  like  the  white  of  the 
egg  it  is  coagulated  by  heat.  This,  of  course,  kills  the 
bacteria.  After  the  thermometer  has  been  in  one  pupil's 
mouth,  and  before  it  is  used  again,  it  should  be  thor- 
oughly rinsed  in  boiling  water  to  kill  all  possible  germs. 
It  may  then  be  dipped  in  cold  water  to  bring  the  mercury 
below  the  temperature  of  the  body.  In  this  way  let  the 
thermometer  be  sterilized*  and  the  mouth  temperatures 
of  several  pupils  be  taken.  Tabulate  your  results  and 
compare. 

Exercise  8.  Fill  a  vessel  with  ice  water.  Feel  the  tem- 
perature with  the  hand.  Set  it  on  the  stove  and  heat  it, 
holding  a  thermometer  in  the  water  and  testing  the  heat 
with  the  hand  from  time  to  time. 

The  temperature  of  the  water  of  a  cold  bath  is  from  33  to 
60  degrees  F. ;  of  a  temperate  bath  from  70  to  85  degrees ;  of 
a  tepid  bath  from  85  to  92  degrees ;  of  a  warm  bath  from 
92  to  98  degrees;  and  of  a  hot  bath  from  98  to  112  degrees. 
Become  familiar  with  the  feel  of  the  water  at  the  different 
temperatures  mentioned. 

Exercise  9.  Study  the  effects  of  various  exposures  made 
by  placing  thermometers  in  the  shade,  in  the  sun,  in  the  wind, 
near  the  ground,  at  an  elevation,  in  the  open  air,  in  some 
secluded  place  in  an  angle  of  the  house,  in  a  well,  in  a  valley, 
on  a  hill,  and  in  other  locations.  In  a  word,  cultivate  the 
habit  of  observation  and  the  power  to  interpret  your  results 
intelligently. 

By  the  experiments  that  we  have  performed  we  have 
learned  that  the  thermometer  is  one  of  the  most  useful 
of  instruments,  a  practical  tool  which  has  frequent  uses 


270  Science  for  Beginners 

in  our  everyday  life.  By  it  we  regulate  the  heating  of 
home  or  office,  and  by  it  the  janitor  of  the  school  or  church 
may  know  whether  he  is  furnishing  just  enough  heat, 
not  too  much  or  too  little,  to  make  people  comfortable. 
By  the  use  of  the  thermometer  in  the  kitchen  we  may 
ascertain  the  proper  temperature  of  the  oven  so  that 
the  best  results  in  baking  may  be  obtained,  and  in  a  time 
of  sickness  the  good  doctor  visits  us  and  by  the  use  of 
his  thermometer  gathers  information  on  which  to  form 
his  judgment  as  to  the  condition  of  the  patient.  Like  a 
good  scientist  he  does  not  guess,  but  accurately  measures 
the  temperature  of  his  patient  in  order  that  he  may 
know. 

Perhaps  you  will  have  enough  interest  in  measuring 
temperatures  to  make  other  experiments. 


CHAPTER   TWENTY-EIGHT 

THE  PHOTOGRAPH 

A  timid  girl  or  an  embarrassed  boy  has  placed  herself 
or  himself  before  a  mysterious  box  with  its  one  eye  and 
has  put  on  a  " pleasant  expression."  There  has  been 
a  sudden  click  of  some  part  of  the  apparatus ;  the  oper- 
ator has  disappeared  into  a  dark  room  and  made  a  few 
passes  over  the  glass  plate,  to  emerge  presently  from 
his  hiding  place  and  announce  with  a  reassuring  smile, 
"It  is  splendid  and  you  can  see  the  proofs  day  after 
tomorrow."  A  negative  has  been  produced  by  the 
photographer  and  from  it  he  will  print  the  positive 
which,  when  properly  finished  and  mounted  upon 
a  card,  is  ready  to  astonish  or  please  the  subject's 
friends. 

Photography  a  complex  process.  Very  few  people 
understand  the  many  changes  which  occur  in  widely 
different  substances  before  a  photograph  is  produced. 
Truly  the  highest  skill  and  ingenuity  of  man  have  been 
exercised  before  the  picture  is  complete,  and  the  ends  of 
the  earth  have  made  their  contributions ;  the  animal, 
vegetable,  and  mineral  kingdoms  have  all  been  drawn 
upon.  Silver  from  the  mines  of  Nevada,  "  pyro  "  from 
the  oak  forests  of  the  Levant,*  sodium  chlorid  from  the 
salt  wells  of  Michigan,  sodium  nitrate  from  the  nitrate 
beds  of  Chile  in  far-away  South  America,  iodin  and  bro- 
min  from  the  ocean,  glass  from  the  factories  of  Europe, 
—  these  and  many  other  products  are  required ;  and  for 
making  both  plate  and  print  there  is  needed  the  mighty 
influence  of  the  light  which  has  made  its  long  journey 

271 


272  Science  for  Beginners 

of  millions  of  miles  (how  many?)  from  the  sun  to  the 
earth. 

We  may  not  explain  away  all  the  mysteries  of  the 
photographic  process,  —  no  one  can  do  this,  —  but  we 
may  gain  much  profit  by  unraveling  some  of  the  ends 
of  the  complex  problem  and  may  learn  the  better  to 
appreciate  that  much  prized  invention  of  the  present 
age,  the  kodak  picture. 

Definition  of  photography.  The  word  "  photograph  " 
is  formed  by  combining  two  Greek  words,  photos,  mean- 
ing "  light,"  and  graphein,  "  to  write."  Literally,  there- 
fore, the  word  means  "  light- writing  "  or  "  writing  by 
the  light."  Photography  is  the  art  of  fixing  upon  a 
sensitive  plate  or  paper,  through  the  agency  of  light,  an 
image  of  any  given  object.  A  review  of  the  history 
of  photography  will  perhaps  serve  as  the  best  introduc- 
tion to  the  subject. 

The  first  camera.  The  first  camera  was  simply  a 
darkened  room  to  which  light  was  admitted  through  a 
single  small  hole  in  the  window  shutter.  When  the  sun 
shone  brightly,  a  faint,  inverted  image  of  the  landscape 
outside  could  be  seen  on  the  white  surface  of  the  wall 
inside.  This  fact  was  discovered  and  used  by  an  Italian 
,  philosopher,  Giambattista  della  Porta,  in  the  last  half 
of  the  sixteenth  century,  although  it  is  claimed  that  the 
same  discovery  had  been  made  by  Roger  Bacon,  who 
lived  in  the  thirteenth  century.  (Who  was  Roger 
Bacon?) 

Exercise  i.  Close  all  the  shutters  of  the  schoolroom 
and  allow  a  ray  of  sunlight  to  pass  in  through  a  tiny  opening. 


The  Photograph 


273 


The  dust  in  the  air,  which 
you  had  not  noticed  before, 
will  make  visible  the  rays 
of  light.  You  can  make 
them  more  plainly  visible 
by  knocking  together  two 
blackboard  erasers,  to  in- 
crease the  number  of  dust 
particles  in  the  air.  Do 
the  rays  of  light  travel  in 
a  straight  line?  Can  you 
see  around  a  corner? 


FIG.  165.    The  camera  obscura. 


Exercise  2.  Allow  the  light  to  fall  on  a  white  wall  or 
hold  a  sheet  of  white  paper  or  cardboard  in  its  path.  Notice 
the  images  of  outside  objects  formed  upon  this  background. 
Because  light  travels  in  straight  lines,  everything  in  the 
picture  is  upside  down.  Consider  carefully  why  this  must 
be  so. 

The  camera  obscura.  The  camera  of  today  has 
certain  improvements  by  which  the  brightness  and 
sharpness  of  the  image  can  be  increased  and  its  size 
regulated.  For  example,  since  the  room  and  the  land- 
scape are  fixed  in  position,  they  cannot  be  adjusted  to 
each  other  so  that  the  image  will  be  of  the  desired  size, 
and  this  difficulty  suggested  the  use  of  a  movable  screen 
on  which  the  image  would  fall.  This  in  turn  suggested 
a  darkened  box  which  could  be  moved  from  place  to 
place  as  desired.  Dealers  in  physical  apparatus  now 
have  for  sale  a  reproduction,  made  for  pupils'  use,  of 
the  first  camera  obscura  (dark  chamber).  It  consists 
of  two  boxes  which  "  telescope  "  on  each  other,  one  box 


274  Science  for  Beginners 

containing  a  pinhole,  the  other  with  a  ground-glass  plate 
(Fig.  165).     A  crude  camera  may  be  made  as  follows: 

Exercise  3.  Take  an  empty  tin  can  without  a  cover. 
Make  a  hole  of  some  size  in  the  bottom  of  the  can.  Paste 
a  piece  of  tin  foil  over  this  opening  and  prick  a  pinhole  in 
the  middle.  Cover  the  open  end  of  the  can  with  a  thin 
tracing  paper  or  cloth.  Turn  the  pinhole  toward  a  candle 
flame,  and  an  image  of  the  flame  will  be  seen  upon  the  paper. 
Notice  that  it  is  inverted  and  that  the  size  of  the  image  de- 
pends upon  the  distance  of  the  pinhole  from  the  candle. 
The  image  will  be  seen  more  plainly  if  a  dark  cloth  is  used 
(after  the  fashion  of  the  photographer)  to  screen  the  eye 
from  the  outside  light.  Learn  by  experience  whether  you 
get  a  clearer  image  when  the  pinhole  is  very  small  or  larger. 

An  improvement  in  the  camera.  Delia  Porta  made  an- 
other important  improvement  upon  the  camera  obscura 
when  he  found  that  by  placing  a  double-convex  lens  in 
the  opening  a  much  brighter  and  more  sharply  denned 
image  was  obtained. 

Exercise  4.  Procure  a  convex  lens  (a  reading  glass  may 
be  used)  and  note  how  it  forms  an  image.  Hold  the  lens 
over  a  printed  page  and  find  by  trial  the  place  where  it  must 
be  held  to  see  well ;  then  notice  that  the  letters  seem  larger 
than  they  really  are.  You  do  not  see  the  letters,  but  rather 
their  image. 

Examine  the  image  on  the  ground  glass  in  the  back  of  a 
camera.  Does  the  lens  of  the  camera  admit  more  light  than 
the  pinhole  in  the  camera  obscura,  or  less  ? 

The  rays  of  light  from  external  objects  enter  the  lens 
and  form  a  bright  image  of  the  object  in  its  natural 
colors,  smaller  in  size  and  in  an  inverted  position.  Figure 


The  Photograph 


275 


1 66  shows  how  such  a  camera  was  first  used.  The  only 
way  to  preserve  the  pictures  produced  was  to  copy  them ; 
so  the  artist  shut  himself 
in  darkness  as  he  worked. 
A  very  complete  or  per- 
fect picture  of  the  object 
was  not  obtained,  but  the 
introduction  of  the  lens 
was  a  great  improve- 
ment, —  one  which  made 
possible  further  progress 
in  the  photographic  art. 

The  photograph.  It  is 
a  matter  of  common  ex- 
perience that  when  the 
skin  is  exposed  to  the  hot 
sun  for  some  time,  it  becomes  darkened  or  "  tanned." 
Some  chemical  action  takes  place  which  changes  its  color. 
The  great  Aristotle  (384-322  B.C.)  noticed  this  fact  and 
recorded  it  in  one  of  his  books.  He  did  not  know  the 
real  significance  of  what  he  had  observed,  —  that  light 
can  cause  chemical  changes ;  but  later  it  was  discovered 
that  light  does  cause  these  changes,  and  this  fact  is  the 
basis  on  which  the  art  of  photography  rests. 

The  other  half  of  the  discovery  was  made  in  1727  by 
J.  H.  Schutze,  a  German,  who  obtained  the  first  actual 
photographic  copy  of  writing  by  placing  the  black  copy 
over  a  mixture  of  chalk  and  silver  nitrate  and  exposing 
it  to  sunlight.  By  doing  this,  he  came  face  to  face  with 
the  basic  principle  of  all  photography,  which  is  that  silver 


An  early  form  of  the  camera. 


276  Science  for  Beginners 

salts  turn  black  when  exposed  to  the  light.  You  may 
observe  the  fact  by  repeating  this  historical  experiment. 
Exercise  5.  Make  a  thin  paste  of  silver  nitrate  and 
powdered  chalk.  Moisten  a  piece  of  filter  paper  with  the 
solution  and  spread  the  paper  out  on  a  flat  surface.  Lay 
some  opaque  object,  like  a  key,  on  the  paper  and  expose  it 
to  the  direct  rays  of  the  sun.  The  light  will  break  down  the 
molecules  of  the  silver  nitrate  that  are  not  protected  from 
the  sunlight  by  the  key,  and  will  form  a  new  compound 
which  is  of  a  different  color. 

In  1802,  Sir  Humphry  Davy  discovered  that  silver 
chlorid  was  much  more  sensitive  to  the  light  than  silver 
nitrate.  We  may  repeat  his  experiment  as  follows : 

Exercise  6.  First  moisten  a  filter  paper  with  a  strong 
solution  of  common  salt  and  then  drop  it  flat  into  a  solution 
of  silver  nitrate. 

AgNOs  +  NaCl  ->  AgCl  +  NaN03 

silver  nitrate  +  sodium  chlorid  — >  silver  chlorid  +  sodium  nitrate 

Silver  chlorid  is  deposited  by  this  process  on  every  part 
of  the  paper. 

Exercise  7.  Take  the  paper  from  the  solution,  spread  it  out 
as  before,  cover  it  with  a  key,  and  expose  it  to  the  sunlight. 

Of  course  your  picture  fades  out,  as  did  those  pro- 
duced by  Davy,  who  could  find  no  way  to  prevent  this. 

The  daguerreotype.  In  1832,  a  Frenchman  named 
Daguerre  discovered  a  method  of  "  fixing  "  the  picture. 
A  copper  plate  was  coated  with  silver  and  highly  polished. 
This  plate  was  then  exposed  to  vapors  of  iodin,  thus 
forming  silver  iodid. 

Ag+^I  -+    Agl 

silver  +  iodin  — >•  silver  iodid 


The  Photograph  277 

The  plate  was  then  placed  in  a  camera,  the  subject  was 
placed  in  position,  and  the  exposure  was  made.  The 
time  of  exposure  was  about  20  minutes.  Next,  the 
plate  was  taken  to  the  dark  room  and  exposed  to  the 
vapors  of  mercury  at  60  or  70  degrees,  and  afterwards 
placed  in  a  solution  of  gold  chlorid  and  sodium  hypo- 
sulfite.  .  By  this  process  a  brilliant  and  very  permanent 
picture  was  produced.  In  this  way  was  begun  one  of 
the  most  marvelous  discoveries  ever  made.  Daguerre 
received  a  pension  of  6000  francs  from  the  French  gov- 
ernment in  appreciation  of  the  fact  that  he  freely  gave 
the  details  of  his  discovery  to  the  world.  Let  some 
pupil  bring  to  the  class  a  good  example  of  a  daguerreo- 
type. Many  of  those  made  more  than  a  half  century 
ago  are  as  bright  and  perfect  today  as  when  first  taken. 

How  modern  photographs  are  made.  The  method  of 
making  a  modern  photograph  is  best  found  out  by  the 
principle  of  "  learning  to  do  by  doing."  When  you  buy 
your  camera,  ask  for  the  circular  of  information  which 
goes  with  it;  and  by  carefully  following  directions  you 
can,  through  practice,  become  an  adept.*  The  chem- 
istry of  the  process  we  shall  explain  in  a  general  way. 

When  you  buy  a  photographic  plate  or  film,  you  re- 
ceive a  square  of  glass  or  a  strip  of  celluloid  *  upon 
which  gelatin*  has  been  evenly  spread  and  in  every 
part  of  which  a  silver  salt,  usually  silver  bromid,  has 
been  suspended.  This  plate  is  placed  at  the  focus  of 
the  lens  of  a  light-proof  camera  (a  camera  obscura) ,  and 
when  the  object  to  be  photographed  has  been  properly 
placed,  the  shutter  opens  for,  it  may  be,  a  small  fraction 


278 


Science  for  Beginners 


of  a  second.  What  hap- 
pens at  this  point  has 
been  illustrated  in  Ex- 
ercises 5  and  6  of  this 
chapter;  the  light  from 
the  object  is  reflected 
into  the  camera  and  falls 
upon  "the  sensitive  gel- 
atin film  on  the  plate. 
Where  the  light  strikes 
the  film  a  change  is 
produced  in  the  silver 
salts,  but  this  change 
cannot  be  observed  by 
the  eye. 

The  next  step  is  taken 
in  the  dark  room  under 
a  red  light,  when  the  pic- 
ture is  developed.  This 
is  accomplished  by  the  use  of  a  reducing  agent  (page  103), 
such  as  pyrogallic  acid  or  hydroquinone.  These  chemicals 
acton  the  silver  salts  that  were  affected  by  the  light,  reduc- 
ing them  to  metallic  silver.  Since  the  action  of  the  light 
is  greater  upon  those  parts  that  have  received  the  stronger 
light  and  less  upon  those  parts  that  have  received  less 
of  the  light,  the  reduced  silver  is  left  upon  the  plate  exactly 
in  proportion  to  the  intensity  of  the  light  that  fell  upon  it. 
In  other  words,  there  will  be  larger  amounts  of  free  silver 
in  the  parts  of  the  film  that  were  exposed  to  a  strong  light, 
and  smaller  amounts  in  the  parts  exposed  to  a  weak  light. 


Eastman  Kodak  Company 
FIG.  167.  The  negative  from  which  the 
positive  shown  in  Figure  168  was  made. 
The  negative  is  dark  where  the  object  was 
light  and  light  where  the  object  was  dark. 


The  Photograph 


279 


The  next  step  is  the 
fixing  of  the  plate.  This 
is  done  by  the  use  of 
"  hypo  "  (sodium  hypo- 
sulfite),  which  dissolves 
out  the  silver  salt  not 
acted  on  by  the  light 
and  the  developer,  but 
leaves  the  free  silver  in 
the  film.  This  makes 
the  plate  light  where 
it  was  not  acted  on  by 
the  light,  and  dark 
where  the  light  and  the 
developer  have  acted  on 
the  silver  so  as  to 
keep  it  on  the  plate. 
After  fixing,  the  plate 
is  thoroughly  washed  in 
water  to  remove  the  "  hypo/'  and,  when  dried,  the 
negative  is  ready  for  use.  If  you  have  carefully  followed 
the  process  to  this  point,  you  will  clearly  see  why  it  is 
called  a  "  negative."  The  plate  is  dark  where  the  object 
was  light  and  light  where  the  object  was  dark. 

The  positive.  The  photograph  is  called  the  "posi- 
tive." The  process  of  making  it  on  a  "  printing  out  " 
paper  is  as  follows  :  A  paper  coated  with  egg  albumen  in 
which  silver  chlorid  has  been  suspended  is  prepared  as 
in  Exercise  6.  The  negative  is  then  placed  over  this 
paper  and  exposed  to  the  light,  which  causes  the  paper 


Eastman  Kodak  Company 
FIG.  1 68.  We  go  into  the  forests  and  fields 
with  the  camera  to  learn  and  carry  home 
the  secrets  of  the  wild  life  to  be  found 
there. 


280  Science  for  Beginners 

to  turn  dark.  The  action  of  the  light  is  in  proportion  to 
the  thickness  of  the  silver  deposit  in  the  different  parts 
of  the  plate  —  the  paper  becomes  dark  where  the  neg- 
ative is  light,  and  prints  light  where  the  negative  is 
dark,  in  which  respect  it  is  like  the  original  object  from 
which  the  picture  was  made.  After  a  proper  exposure, 
the  print  is  carried  through  the  fixing  process  in  the 
same  way  that  the  negative  was.  The  color  of  the  pic- 
ture may  be  improved  by  toning  the  print  in  a  solu- 
tion of  gold  chlorid.  After  this  the  picture  is  washed, 
dried,  and  mounted  in  an  album  or  upon  a  suitable  card. 

When  a  developing  paper  is  used,  the  process  of 
making  a  print  is  the  same  as  that  of  making  a  neg- 
ative. After  exposure  to  the  light  the  paper  is  de- 
veloped, fixed,  washed,  and  dried. 

The  present  an  age  of  photography.  One  member 
of  nearly  every  family  is  almost  certain  to  possess  a 
camera  of  some  kind  or  other,  and  "  snapshots  "  are 
taken  of  the  children  and  friends  in  their  familiar 
surroundings.  These  pictures  should  be,  and  are,  care- 
fully preserved  for  the  great  value  they  will  have 
in  future  years.  The  camera  is  taken  on  our  pic- 
nics and  other  excursions  to  catch  and  preserve  the 
beauties  of  natural  scenery  and  to  enable  us  to  recall 
pleasant  incidents  in  our  lives.  We  go  into  the  forests 
and  fields,  not  with  a  gun  as  formerly,  but  with  a 
camera,  to  learn  and  carry  home  the  secrets  of  the  wild 
life  to  be  found  there.  We  point  the  camera  at  the  stars 
and  from  the  photographs  thus  obtained  are  able  to 
learn  many  facts  we  could  not  glimpse  through  the  tele- 


The  Photograph  281 

scope.  We  photograph  the  sun  or  the  moon,  an  eclipse 
or  a  comet,  or  capture  a  stroke  of  lightning  on  a  kodak 
film. 

The  art  of  photography  has  many  valuable  exten- 
sions into  industrial  and  commercial  life.  The  architect 
makes  copies  of  his  plans  by  the  "  blueprint  "  method 
of  photography.  He  makes  successive  photographs  of 
a  building  that  is  being  erected  to  show  the  progress 
which  the  contractor  is  making  in  his  work.  By  the 
various  processes  of  photo-engraving,*  pictures  are  re- 
produced for  newspapers  and  books  so  that  photographs 
of  all  the  world  are  laid  before  our  eyes,  and  the  works 
of  great  painters  are  reproduced  so  that  every  touch  of 
the  brush  is  clearly  seen  in  the  copy.  Color  photog- 
raphy is  now  possible;  and  X-ray  photographs  are 
made,  showing  the  bones  and  other  internal  parts  of 
the  human  body. 

The  crowning  achievement  in  the  science  and  art  of 
photography  is  the  motion  picture.  This  is  made  by 
taking  repeated  pictures  of  people  and  animals  in  action 
or  of  automobiles  or  other  objects  in  motion,  and  then 
by  the  use  of  proper  projecting  apparatus  reproducing 
these  actions  and  scenes  exactly  as  they  occurred  in  the 
first  place.  This  has  been  made  possible  by  the  manu- 
facture of  very  sensitive  films  and  the  invention  of  a 
shutter  by  which  an  exposure  of  from  T^TT  to  roW  of  a 
second  may  be  made. 


CHAPTER  TWENTY-NINE 

THE  LIGHT 

IN  the  last  chapter  we  learned  about  the  art  of  photog- 
raphy, and  how  light  is  made  to  paint  the  most  marvel- 
ous pictures  for  our  enjoyment  and  use.  Our  attention 
was  given  to  the  picture,  however,  and  we  took  little 
thought  of  the  light  which  does  the  work.  In  this  chapter 
we  shall  study  the  light  itself.  We  have  already  learned 
that  it  is  the  source  of  heat  (page  251)  and  that  it  pro- 
duces chemical  action  (page  275),  but  what  we  have  not 
yet  asked  is,  What  is  light  and  how  does  it  produce 
these  effects  ?  Let  us  see  what  can  be  found  out  about 
this  highly  interesting  subject. 

The  nature  of  light.  Light  does  not  seem  to  be  mat- 
ter; as  far  as  we  know  it  has  no  weight,  and  it  leaps 
across  space  and  passes  through  glass  and  other  materials 
in  a  way  that  we  should  not  expect  matter  to  do.  Does 
it  not  seem  more  like  sound,  which  is  waves  of  motion  in 
the  air,  and  is  it  possible  that  light  also  is  waves  in  the 
air?  We  can  answer  this  question  by  observing  ex- 
periments that  have  already  been  performed  for  us. 

Light  comes  to  us  from  the  sun.  How  many  miles 
is  it  to  the  sun?  How  high  does  the  atmosphere  ex- 
tend above  the  surface  of  the  earth?  Is  there  air  all 
the  way  from  the  sun  to  the  earth  through  which  a 
wave  could  travel  to  us? 

An  incandescent  electric-light  globe  has  had  practically 
all  the  air  pumped  out  of  it.  Look  through  such  a  globe 
at  some  object.  Does  the  light  pass  through  it?  Is  the 
light  able  to  travel  out  from  the  luminous  filament  to 

282 


The  Light  283 

the  walls  of  the  lamp?  Could  it  do  this  if  it  depended 
upon  the  air?  Review  the  exercises  on  page  237,  and 
find  the  proof  that  light  cannot  be  waves  in  the  air. 

A  simple  and  satisfactory  explanation  of  the  nature 
of  light  has  not  been  easy  to  find,  but  scientists  believe 
that  all  space,  even  the  spaces  among  the  molecules  of 
bodies  of  matter,  is  filled  with  an  invisible  substance 
which  they  have  called  ether,  and  that  light  is  waves  in 
the  ether  that  can  be  recognized  by  the  eye.  When  these 
waves  dash  against  the  retina  of  the  eye,  they  start  im- 
pulses to  the  brain  that  give  us  the  sensation  of  light. 
When  they  strike  the  photographic  plate,  they  break 
down  and  change  the  silver-bromid  molecules  in  the 
plate ;  and  if  with  a  lens  a  great  number  of  these  little 
waves  are  all  turned  toward  one  point  on  a  piece  of 
paper,  they  beat  upon  it  until  the  paper  takes  fire 
(page  251). 

Light  travels  at  the  tremendous  velocity  of  186,300 
miles  per  second.  It  comes  from  the  sun  to  the  earth 
in  about  8  minutes,  and  it  would  take  only  one  seventh 
of  a  second  to  go  around  the  earth. 

Light  and  motion.  Sir  William  Crookes,  the  eminent 
English  scientist,  invented  an  interesting  piece  of  ap- 
paratus known  as  the  radiometer.*  It  consists  of  a 
framework  which  is  so  nicely  poised  that  it  rotates 
with  the  greatest  freedom.  It  is  inclosed  in  a  glass 
bulb  from  which  practically  all  the  air  has  been  removed. 
When  exposed  to  the  sunlight,  the  little  mill  begins  to 
rotate.  The  more  intense  the  light  and  heat  the  faster 
it  whirls  about.  Motion  is  produced  by  the  light.  We 


284 


Science  for  Beginners 


shall  come  back  to  this  experiment 
as  we  study  a  later  chapter. 

Reflection  of  light.  At  this  point 
we  need  an  experiment  which  almost 
every  boy  has  tried  before,  for  the 
purpose  of  having  a  bit  of  fun  or 
playing  a  trick  upon  some  one.  We 
may  still  have  fun  with  it  if  we  put 
it  to  a  more  scientific  purpose. 

Exercise  i.  Hold  a  small  mirror  in 
the  path  of  a  ray  of  sunlight  and  notice 
the  direction  from  which  the  ray  has 
come  and  also  the  direction  it  takes 
after  it  leaves  the  mirror.  This  is  best 
done  in  the  dark  room. 

FIG.  169.    A  radiometer.  What    Y™    have    observed    is    an 

example  of  the  reflection*  of  light. 
The  light  waves  strike  the  mirror  and  rebound,  or  are 
thrown  back,  as  a  ball  bounds  back  when  it  is  thrown 
obliquely  upon  the  ground  or  sidewalk.  The  ray  of  light 
coming  to  the  mirror  is  called  the  incident  ray,  and  the 
ray  leaving  it  the  reflected  ray. 

Exercise  2.  Place  your  lead  pencil  on  the  spot  where  the 
ray  of  light  strikes  the  mirror  and  make  the  pencil  perpen- 
dicular to  the  mirror  at  that  point.  Notice  that  the  incident 
and  reflected  rays  are  on  opposite  sides  of  the  perpendicular. 
Perhaps  you  will  be  able  to  satisfy  yourself  that  the  angle* 
which  the  incident  ray  makes  with  the  perpendicular  is 
exactly  equal  to  the  angle  which  the  reflected  ray  makes 
with  the  perpendicular. 


The  Light 


285 


FIG.  170.    The  angle  of  incidence  is  equal 
to  the  angle  of  reflection. 


The  above  experiment 
can  be  better  performed 
by  laying  a  mirror  on  the 
floor  in  a  dark  room 
and  using  light  from  a 
small  opening  or  from  a 
lighted  candle.  Figure 
1 70  will  show  you  what 
you  may  observe  if  you 
make  the  experiment  in  this  way.  The  line  PB  is  per- 
pendicular to  the  mirror  at  the  point  of  incidence  B. 
The  angle  of  incidence  is  the  angle  IB P,  and  the  angle 
of  reflection  is  the  angle  PER.  These  two  angles  are 
equal,  and  the  law  holds  good  whenever  the  reflecting 
surface  is  perfectly  polished.  The  law  of  the  reflection 
of  light  is  that  the  angle  of  incidence  is  equal  to  the 
angle  of  reflection. 

Exercise  3.  Look  into  a  mirror  and  note  the  image  of 
some  object  other  than  yourself.  Without  changing  your 
position  or  looking  around,  see  if  you  can  accurately  locate 
the  position  of  the  object  itself.  Do  not  look  at  the  object 
until  you  have  described  its  position,  in  words,  to  your 
teacher  or  classmates. 

Exercise  4.  Examine  your  own  image*  in  a  mirror. 
Are  the  right  and  left  sides  reversed?  Get  your  answer  by 
thinking  on  which  side  your  right  and  left  hands  would  be 
if  you  turned  round  and  faced  the  same  way  that  the  image 
is  facing. 

Exercise  5.  Look  again  at  your  image  in  a  mirror.  Note 
that  it  seems  to  be  exactly  as  far  behind  the  mirror  as  you 
are  in  front  of  the  mirror.  Advance  toward  the  mirror  and 


286 


Science  for  Beginners 


ft i  ^ 


FIG.  171.    The  image  appears  to  be  as  far  behind  the  mirror  as  the  object  is 
in  front  of  it. 

walk  backward  from  it.  Does  your  image  seem  to  advance 
and  retreat  in  the  same  way  ? 

A  second  important  law  in  the  reflection  of  light  is 
that  the  image  appears  to  be  as  far  behind  the  mirror 
as  the  object  is  in  front  of  it. 

Exercise  6.  Lay  the  mirror  on  the  table,  in  a  room  that 
is  not  darkened,  and  place  upon  it  a  glass  of  water  or  other 


The  Light 


287 


object.  Notice  that  the  glass  seems  to  stand  upon  another 
one  that  is  bottom  side  up.  Notice  that  every  point  in  the 
image  seems  to  be  just  as  far  behind  the  mirror  as  the  corre- 
sponding point  of  the  object  is  in  front  of  it,  and  also  that 
the  image  is  of  the  same  size  as  the  object.  From  the 
principle  that  we  learned  in  the  last  experiment,  can  you 
explain  why  the  image  is  wrong  side  up  ? 

An  enjoyable  scientific  game.  These  two  principles 
(what  are  they?)  of  the  reflection  of  light,  if  you  learn  to 
recognize  them,  will  lead  to  endless  enjoyment  as  you  notice 
the  curious  antics  played  by  the  light  wherever  there  are 
bright  reflecting  surfaces,  such  as  plate-glass  windows, 
mirrors  in  hotels  and  restaurants,  polished  metal  or  wood 
on  boats  and  cars,  and  the  liquid  mirrors  that  nature  has 
provided  in  the  great  out-of-doors.  Make  it  a  part  of  the 
pleasure  of  your  ride  on 
the  cars  to  trace  out  the 
place  of  the  objects  which 
form  the  images  you  see ; 
such  a  study  will  make 
even  more  beautiful  the 
inverted  landscapes 
buried  deep  in  the  heart 
of  pond  or  pool. 

Refraction*  of  light. 
We  are  now  to  deal  with 
a  new  word  and  the  idea 
for  which  it  stands. 
Begin  with  a  visit  to  the 
dictionary. 


FIG.  172.    The  stick  appears  to  be  bent 
where  it  emerges  from  the  water. 


288  Science  for  Beginners 

Exercise  7.  Thrust  a 
stick  obliquely  into  a  pail 
of  water.  The  stick  ap- 
pears bent.  Is  it  bent? 
Be  sure  sometime  to  visit 
a  river,  lake,  or  pond,  and 
perform  the  same  experi- 
FIG.  173.  When  the  vessel  is  filled  with  ment  under  much  more 

water,  the  coin  comes  into  view.  favorable  Conditions. 

If  you  have  had  any  experience  with  water,  you  know 
that  it  is  difficult  to  tell  exactly  where  an  object  is  when 
it  is  under  water.  Only  an  experienced  person  can  spear 
a  fish,  and  a  pond  is  always  deeper  than  it  looks.  Does 
something  happen  to  the  light  as  it  comes  from  beneath 
the  water  to  our  eyes?  Let  us  try  some  other  experi- 
ments. 

Exercise  8.  Look  obliquely  into  a  pail  of  water  and  then 
place  your  finger  on  the  outside  of  the  pail  where  the  bottom 
seems  to  be.  What  mistake  did  you  make?  Why  is  water 
always  deeper  than  it  seems  to  be  ? 

Exercise  9.  Take  a  deep  dish  which  is  empty  and  place 
a  bright  coin  on  the  bottom.  Take  your  stand  so  that  you 
can  just  see  the  farther  edge  of  the  coin  over  the  edge  of  the 
dish.  Now,  keeping  your  eye  at  the  same  place,  have  some 
one  fill  the  dish  with  water.  You  will  see  the  coin  gradu- 
ally brought  into  full  view. 

The  coin  seems  to  have  moved  in  the  water,  but  this 
is  not  the  case.  A  diagram  will  explain  what  has  hap- 
pened (Fig.  1 73) .  The  ray  of  light  from  the  coin  A  passed 
in  a  straight  line  to  D ;  but  when  the  dish  was  filled  with 
water  the  ray  was  bent,  or  refracted,  as  it  left  the  water 


The  Light  289 

at  E  and  passed  into  the  eye 

at  C.     As  the  eye  seems  to 

see  an  object  in  a  straight 

line  with  the  ray  that  enters 

the  eye,  it  seemed  in  this 

case  to  see  the  coin  at  B. 

Hence   the    bending  of  the 

rays  of  light  as  they  pass  FlG-  X74- 

out  of  the  water  causes  the  coin  to  seem  to  be  more 

elevated  than  it  really  is  and  to  seem  to  be  moved 

toward  the  farther  side  of  the  dish. 

This  bending  of  the  ray  of  light  is  called  refraction. 
It  occurs  when  light  passes  from  one  substance,  or 
medium,  into  another  of  different  density,  as  from  water 
to  air  or  from  air  to  water.  You  will  learn  more  about 
refraction  when  you  go  further  in  your  study  of  physics. 

Refraction  of  light  by  glass.  Many  substances  be- 
sides water  refract  light,  a  fact  which  can  be  well  shown 
with  a  triangular  glass  prism.*  One  that  is  6  inches 
long  and  has  faces  that  are  i|  inches  wide  will  cost 
about  40  cents.  A  substitute  may  be  found  in  a  pendant 
from  a  glass  chandelier,  or  a  cut-glass  bottle  stopper  of 
3  or  6  sides.  As  you  work  with  the  prism  you  may 
notice  a  play  of  colors  in  the  light  that  passes  through 
it.  The  study  of  this  will  be  deferred  until  near  the 
end  of  the  chapter. 

Exercise  10.  Taking  the  prism  in  both  hands,  hold  it 
before  your  eyes  so  that  the  lower  face  is  horizontal  or  level 
with  the  floor.  In  this  position  look  through  it  into  the  eyes 
of  another  person  so  that  you  see  them  clearly. 


290  Science  for  Beginners 

When  you  have  established  the  proper  position  for  the 
prism,  you  can  study  the  path  of  the  ray  of  light  which  passes 
from  your  friend's  eye  through  the  prism  and  then  on  to 
your  eye.  You  may  have  to  practice  with  the  prism  some 
time  before  you  succeed  with  this  experiment. 

If  the  prism  were  not  in  the  way,  the  path  of  the  light 
would  be  perfectly  straight;  for,  as  you  have  learned, 
light  travels  in  straight  lines  through  the  air.  Here, 
however,  its  path  is  in  two  media,*  the  air  and  the  glass. 
On  this  account  it  is  bent  from  its  path,  just  as  it  is  bent 
when  it  passes  from  water  to  air  or  from  air  to  water. 
Figure  174  will  help  you  to  understand  what  has  hap- 
pened. The  rays  of  light  from  A  strike  the  prism  at  7, 
but  instead  of  going  on  in  a  straight  line,  they  are  bent 
both  when  they  enter  and  when  they  leave  the  prism. 
Since  light  usually  comes  to  the  eye  in  a 
straight  line,  the  mind  judges  that  it  has  done 
so  in  this  case  also.  The  candle  therefore 
appears  to  be  at  B.  Copy  Figure  174  on 
the  blackboard  and  explain  it  to  the  class. 

A  study  of  the  reading  glass.      Borrow 
the  large  reading  glass  from  Grandmother, 
or  use  the  one  that  may  be  furnished  from 
the  physics  laboratory.    It  should  be  convex 
FIG.  175-  Dia-   on  both  sides. 

gram  to  show 

how  a  lens  con-       Exercise  ii.    Repeat  Exercise  16  on  page 
vexoneachside    2-o      Note  that  au  the  rays  of  ^ght  are  bent 

resembles  two       J 

prisms     with   inward  so   that  they  fall   on   one  spot  upon 
their      bases   the  paper.    This  spot  is  called  the   focus  of 

placed    to-  

gether.  the  glass. 


The  Light 


291 


Why  does  the  glass 
turn  all  the  rays  of  light 
inward  ?  If  we  go  back 
to  the  triangular  prism 
for  a  brief  review,  we 
may  find  a  partial  ex- 
planation of  the  focus 
of  the  reading  glass. 
As  we  traced  the  path  of 
the  ray  of  light  through 
the  prism,  we  noticed 
that  the  bending  of  the 
ray  was  in  both  cases 
in  a  direction  toward 
the  base  of  the  prism. 

This  being  SO,  let  US  ask     FIG.  176.    The  image  formed  by  the  lens  is 

ourselves   what    would 

happen  if  two  such  triangular  prisms  were  placed  with 
their  bases  together.  Is  it  not  clear  that  all  the  rays 
of  light  from  a  given  point  of  the  object  which  falls 
upon  both  prisms  would  be  gathered  together  at  a  focus 
on  the  other  side?  Figures  174  and  175  will  help  you 
to  understand  the  resemblance  between  the  lens  of  a 
reading  glass  and  two  prisms  placed  base  to  base. 

Exercise  12.  Throw  an  image  of  a  burning  candle  on  a  white 
wall  or  on  a  piece  of  white  cardboard  in  the  manner  shown  in 
Figure  176.  Is  the  image  upside  down  ?  Notice  that  the  lens 
will  form  a  clear  image  when  it  is  held  in  only  one  place. 

How  images  are  formed  by  lenses.  How  does  a  lens 
form  an  image?  Visit  a  motion-picture  theater  or  at- 


Science  for  Beginners 


FIG.  177.    Diagram  showing  how  an  image  is  formed  by  a  lens. 

tend  a  stereopticon  exhibition  and  see  if  you  can  study 
out  this  problem.  As  you  well  know,  there  are  no  real 
pictures,  but  only  images,  on  the  screen.  These  are 
formed  by  placing  the  films  or  slides  in  front  of  a  strong 
light  and  then  allowing  the  light  to  pass  through  a  convex 
lens  to  the  screen.  All  the  light  which  shines  through 
one  point  of  the  film  is  focused  in  one  point  on  the  screen, 
so  that  the  complete  image  on  the  screen  is  made  up  of 
an  innumerable  number  of  images  of  all  the  different 
parts  of  the  film.  Thus  all  the  rays  from  a  tiny  flower 
in  the  film  are  brought  together  to  make  a  flower  on  the 
screen,  the  rays  from  each  twig  and  leaf  on  a  tree  are 
focused  hi  their  own  place  to  form  an  image  of  the  tree, 
and  the  light  from  the  eyes,  nose,  mouth,  cheeks,  chin, 
forehead,  and  hair  of  each  actor  is  brought  together  in 
such  a  way  as  to  build  up  an  image  of  the  face. 

If  the  explanation  given  above  is  not  clear,  examine 
Figure  177  and  note  how  all  the  rays  of  light  from  one 
point  are  brought  together  in  one  point  to  form  an  image. 
Then  imagine  the  film  in  the  motion-picture  machine 
to  be  composed  of  thousands  of  separate  points  and  that 


The  Light 


293 


an  image  of  each  is  be- 
ing formed,  and  you 
will  have  the  key  to 
the  explanation  you  are 
seeking.  Is  the  film 
inserted  in  a  motion- 
picture  machine  upside 
down?  If  so,  why  is 
this  necessary  ? 

Magnifying  glasses. 
The  pictures  on  a  mo- 
tion-picture machine 
are  not  more  than  an 
inch  in  diameter.  The 
image  on  the  screen 
may  be  10  feet  across. 
Clearly  it  is  possible 
by  means  of  lenses  to 
make  objects  appear 
much  larger  than  they 
really  are. 

Exercise  13.  Hold  a  reading  glass  over  the  page  of 
your  book.  At  first  you  may  see  nothing.  Hold  the 
glass  close  to  the  print  with  your  eyes  at  some  distance 
from  the  glass.  Then  gradually  move  the  glass  away 
from  the  page  and  closer  to  your  eye.  Notice  that  the 
glass  magnifies  the  letters  and  makes  them  appear  nearer  to 
the  eye. 

Microscopes*  and  telescopes.*  First  of  all,  learn  to 
appreciate  the  literal  meaning  of  these  words.  Your 


FIG.  178.     A  microscope. 


294  Science  for  Beginners 

unabridged  dictionary  will  tell  you  that  the  Greek  word 
micro  means  "  small  "  ;  that  the  word  tele  means  "  far  " 
or  "  far  off  " ;  and  that  skopein  means  "  to  look  at." 
What  do  the  two  words  at  the  head  of  this  paragraph 
mean? 

Microscopes  and  telescopes  are  made  by  placing  several 
lenses,  similar  to  the  one  you  have  examined,  in  such  a 
relation  to  each  other  that  very  great  magnifying  power 
is  produced.  Sometime  when  you  have  a  chance  to 
look  through  a  great  telescope  you  will  see  how  it  seems 
to  bring  the  moon  or  other  distant  object  very  much 
nearer.  A  pair  of  opera  glasses  will  help  you  to  under- 
stand this.  The  best  microscopes  magnify  about  two 
thousand  diameters  and  bring  into  view  hundreds  of  in- 
teresting objects  that  are  wholly  invisible  to  the  naked 
eye.  How  tall  should  you  appear  if  you  were  viewed 
through  such  a  microscope  ?  It  will  be  a  very  useful  ex- 
ercise to  spend  some  time  in  becoming  familiar  with  the 
many  wonders  to  be  revealed  by  the  microscope. 

The  human  eye.  The  most  wonderful  of  all  optical* 
instruments  is  the  human  eye.  In  front  it  has  a  trans- 
parent window  called  the  cornea,  and  behind  the  cornea 
a  crystalline  lens,  which  focuses  the  rays  of  light  and 
forms  images  of  the  objects  that  we  see  on  the  retina.  In 
the  retina  are  the  ends  of  the  fibers  of  the  optic  nerve ; 
when  images  fall  on  the  retina  the  nerve  fibers  are  stimu- 
lated and  messages  started  to  the  brain.  When  these 
reach  the  brain  they  cause  the  sensation  of  sight  and 
give  us  information  about  the  objects  that  we  see.  It 
is  a  curious  fact  that  only  light  waves  can  cause  the  eye 


The  Light 


295 


FIG.  179.    A  section  through  the  eye. 

to  see,  and  that  only  through  the  two  eyes  can  the  light 
make  its  impression  on  that  most  wonderful  mechanism, 
the  human  brain. 

Spectacles.  In  Exercise  12  you  found  that  a  clear 
image  was  formed  only  when  the  lens  was  at  a  cer- 
tain point.  The  image  in  the  eye  is  clear  only  when 
the  retina  is  at  a  certain  distance  behind  the  lens, 
and  some  eyes  are  too  long  or  too  short  for  clear  sight. 
Sometimes  the  difficulty  is  that  the  rays  of  light  cross 
before  they  get  to  the  retina ;  sometimes  they  have  not 
yet  come  to  a  focus  when  the  retina  is  reached.  In 
either  case,  the  image  is  blurred  and  sight  is  indistinct. 

The  remedy  for  these  and  certain  other  troubles  is 


296  Science  for  Beginners 


FIG.  180.    Diagram  showing  the  shape  of  a  normal  eye  (A),  a  far-sighted  eye 
(JB),  and  a  near-sighted  eye  (C). 


to  put  spectacles  in  front  of  the  eyes  that  will  help  focus 
the  rays  of  light  so  that  the  image  will  be  formed  exactly 
on  the  retina.  Figure  181  shows  the  kind  of  lens  that 
is  used  on  far-sighted  eyes.  Other  kinds  of  lenses  must 
be  used  when  the  eye  is  too  long  or  when  there  are  other 
defects  in  the  shape  of  the  eye  or  in  the  lens.  Eyes 
that  need  glasses  should  be  fitted  with  them ;  for  many 
persons  suffer  from  headaches,  nausea,  and  nervous 
troubles  because  the  sight  is  not  clear  or  because  the 
eyes  are  being  strained  to  make  it  clear.  Only  a  skilled 
eye  specialist  should  attempt  to  fit  glasses ;  it  is  a  deli- 
cate task  to  adjust  them  so  as  to  correct  exactly  all  the 
defects  that  may  be  in  a  pair  of  eyes. 

The  solar  spectrum.  We  have  now  to  study  one  of 
the  most  wonderful  and  interesting  facts  about  light. 

Exercise  14.  Take  the  prism  to  the  dark  room  and  place 
it  in  the  path  of  a  beam  of  sunlight  from  the  outside.  Hold 
a  white  cardboard  beyond  the  prism  or  allow  the  light  to 
strike  the  white  wall  of  the  room.  We  shall  find  that  the 
ray  not  only  is  bent  from  its  course,  but  that  it  is  wonder- 
fully broken  up  into  a  number  of  bright  bands  of  color,  the 


The  Light  297 


FIG.  181.  Diagram  showing  how  glasses  bring  the  rays  of  light  to  a  focus  on 
the  retina  of  a  far-sighted  eye.  The  dotted  line  represents  the  path  the  rays 
would  have  taken  if  they  had  not  been  bent  by  the  lens. 

colors  of  the  solar  spectrum.*  These  colors  are  red,  orange, 
yellow,  green,  blue,  and  violet. 

What  is  the  explanation  of  this  curious  change  which 
the  prism  has  produced  upon  the  light  ?  Simply  this : 
light  waves  are  of  different  lengths.  The  red  waves  are 
the  longest  and  the  orange  next  longest ;  then  come  the 
yellow,  green,  and  blue  in  the  order  of  length,  and  last 
the  violet  waves,  which  are  the  shortest  of  all.  In  pass- 
ing through  the  prism  the  shorter  waves  are  refracted, 
or  bent,  more  than  the  longer  waves;  thus  the  violet 
rays  are  refracted  the  most  and  the  red  the  least.  You 
will  see  that  because  of  this  fact  the  different  waves  that 
pass  through  the  prism  fall  on  the  wall  or  the  cardboard 
in  different  places  and  thus  the  colors  are  separated. 
This  is  called  dispersion  of  light. 

The  rainbow.  We  will  close  our  present  work  on 
light  with  a  study  of  that  beautiful  object,  the  rainbow. 
A  number  of  facts  are  to  be  observed. 

Exercise  15.  This  is  an  exercise  which  can  be  carried 
out  only  at  certain  times,  for  the  sun  must  be  shining  and 


298  Science  for  Beginners 


FlG.  182.     Diagram  illustrating  the  dispersion  of  light  by  the  prism.     The 
short  violet  waves  are  refracted  most  and  the  long  red  waves  least. 

the  rain  falling  at  the  same  time.  At  what  time  of  day  will 
the  rainbow  be  in  the  east?  When  in  the  west?  Can  you 
face  the  sun  and  see  the  rainbow  at  the  same  time?  Is  the 
bow  a  part  of  a  perfect  circle  ? 

What  two  colors  are  the  most  prominent  in  the  bow? 
Which  of  these  is  on  the  inside?  Which  is  on  the  outside? 
Can  you  detect  the  other  colors  of  the  solar  spectrum  lying 
between  these  two? 

Here  is  a  clear  case  of  the  dispersion  of  light  into  its 
prismatic  colors.  Now  recall  the  method  of  causing 
this  dispersion,  as  you  have  learned  it.  What  acts  as 
the  prism  in  this  case  ?  A  drop  of  water  disperses  the 
light ;  in  fact,  every  drop  of  water  that  is  falling  acts  as 
a  refracting  prism.  A  ray  of  light  enters  the  drop  and  is 
refracted,  striking  the  inside  surface  of  the  drop  on  the 
opposite  side.  It  is  reflected  back  upon  its  course,  and  as 
it  passes  out  of  the  drop  is  again  refracted.  Thus  the 
colors  are  separated  from  each  other.  Each  drop  will 
form  a  perfect  spectrum,  but  only  one  of  the  colors  may 
come  to  the  eye  of  the  observer ;  other  drops  will  send 
the  other  colors,  until  a  perfect  bow  is  produced. 


The  Light  299 

Sometimes  a  second  larger  rainbow,  known  as  the 
secondary  bow,  is  seen  outside  the  primary  bow.  In 
this  the  colors  are  reversed,  the  violet  being  on  the  inside 
and  the  red  on  the  outside. 

Other  facts  about  light.  White  is  a  mixture  of  all 
colors.  Black  is  the  absence  of  light.  The  page  of 
your  book  is  white  because  it  reflects  all  kinds  of  light 
waves  to  your  eyes.  The  letters  on  the  page  are  black 
because  they  absorb  all  the  waves  and  send  nothing  to 
your  eyes.  A  red  light  appears  red  because  the  glass 
allows  the  red  waves  to  pass  through  and  stops  the  other 
waves.  The  grass  is  green  because  it  reflects  the  green 
waves  and  absorbs  the  other  waves  that  come  to  it  from 
the  sun.  In  the  lights  and  shadows  that  play  about 
you;  in  the  colors  of  flames  and  of  the  stars;  in  the 
light  that  shines  through  stained  windows  and  colored 
lamps ;  in  the  colors  of  sky  and  water  and  of  fruits  and 
flowers;  and  in  the  tints  found  in  books  and  pictures, 
material  for  a  hundred  lessons  is  at  hand.  Each  day 
experiments  will  perform  themselves  for  you;  with  no 
effort  on  your  part  the  results  will  leap  into  your  eyes. 
Is  your  brain  asleep,  or  is  it  alive  to  all  that  comes  to  it 
through  the  windows  of  the  mind  ? 


CHAPTER  THIRTY 

THE  MARINER'S  COMPASS 

"AND  when  neither  sun  nor  stars  appeared  for  many 
days,  all  hope  that  we  should  be  saved  was  lost."  So 
Luke,  the  companion  of  Paul,  wrote 
of  the  time  when  they  were  over- 
taken by  a  storm  at  sea,  and  his 
words  picture  to  us  the  terror  that 
the  sailors  of  those  days  had  of 
being  lost  upon  the  deep.  They 
FIG.  183.  A  common  steered  their  course  by  observa- 

form    of   compass.     The  .  .  . 

card  is  turned  about  until  tions    on    the  sun    and  stars,   and 

the  symbol  for  north  is  when  these  'were  hidden  by  clouds 

:±.' Thnr^  all  sense  of  direction  was  gone  and 

tions  can  then  easily  be  the    helmsman    was    as    likely    to 

determined.  steer  ^  ^   iQWSild    the    rocks    Qf 

a  hostile  coast  as  toward  a  safe  port. 

Now  all  this  has  changed,  and  men  strike  out  boldly 
across  the  vast  expanse  of  the  ocean;  for  they 
carry  with  them  an  instrument  known  as  the  com- 
pass,  which  through  fair  weather  and  foul  points  to  the 
north  and  thus  enables  them  to  know  the  direction  of 
their  course. 

The  compass.  The  compass  was  introduced  into 
Europe  about  the  twelfth  century  and  has  long  been 
used  by  mariners,  surveyors,  travelers,  and  others. 
The  essential  parts  of  it  are  a  delicately  poised  magnetic 
needle,  and  a  compass  card  on  which  are  marked  the 
" points  of  the  compass."  The  needle  is  free  to  turn  in 
any  direction  and  always  points  approximately  to  the 

300 


The  Mariner's  Compass  301 

north.     In  the  larger  compasses  the  card  is  attached  to 

the  needle  and  turns  with  it,  but  in  small  compasses  the 

card  is  under  the  needle 

and  must  be  turned  by 

hand.     The  needle  and 

the  point  marked  north 

on  the  card  will  always 

point  toward  the  north, 

and  from  this  the  actual 

direction  in  which  the 

,  .  ,  .  FIG.  184.     A  mariner's  compass. 

ship  or   the   person   is 

going  may  easily  be  determined.  The  card  is  divided 
into  32  equal  parts  by  lines  drawn  from  the  center, 
each  part  containing  11°  15'.  How  many  degrees  are 
there  in  a  complete  circle  ?  Study  the  system  of  names 
on  the  card  that  indicates  direction  (Fig.  183).  A  small 
compass  may  be  purchased  at  a  jeweler's  at  a  low  cost. 
The  mariner's  compass.  For  use  upon  ships,  one 
addition  must  be  made  to  the  common  compass.  In 
order  that  the  needle  may  always  be  in  a  horizontal 
position  and  be  free  from  jarring  caused  by  the  tramp 
of  the  sailors  and  the  motion  of  the  ship,  the  box  is 
suspended  in  the  gimbals,  as  is  shown  in  Figure  184. 
The  bowl  is  hung  by  two  pivots  (A)  on  the  opposite 
sides  of  a  brass  ring  (C,  D)  which  surrounds  it.  The 
brass  ring  is  itself  balanced  on  two  pivots  on  upright 
supports  (£,  £).  It  will  be  seen  that  whatever  position 
the  supports  are  in,  the  box  maintains  its  upright  posi- 
tion. Study  Figure  184  and  make  sure  that  you  under- 
stand why  this  is  the  case, 


302  Science  for  Beginners 

Exercise  i.     Bring  a  piece  of  steel,  as  a  bunch  of  keys  or 
a  hammer,  near  the  needle  of  the  compass  and  note  how 


FIGS.  185  and  186.    A  bar  magnet  and  a  horseshoe  magnet. 

the  needle  of  the  compass  is  disturbed.  This  will  show  you 
why  surveyors  and  navigators*  are  careful  to  keep  all  forms 
of  iron  away  from  the  compass. 

The  lodestone.  At  an  early  date,  people  living  near 
a  city  of  Asia  Minor  noticed  that  a  certain  kind  of 
iron  ore  possessed  the  power  to  attract  small  pieces  of 
iron.  They  named  this  ore  magnetite*  after  the  name  of 
their  city.  Beds  of  magnetite  are  found  in  the  Adi- 
rondack Mountains  of  New  York  and  in  Pennsylvania, 
Virginia,  and  North  Carolina.  Deposits  of  magnetite 
are  known  also  in  Minnesota,  Colorado,  Utah,  and 
California. 

A  common  name  for  magnetite  is  lodestone,  or 
leading  stone.  If  a  piece  of  it  is  hung  by  a  string,  it 
will  swing  about  until  it  indicates  north  and  south. 
This  fact  was  discovered  very  early,  and  the  needles  of 
the  early  compasses  were  made  of  this  material.  A 
piece  of  magnetite  may  be  purchased  for  a  small  sum 
from  a  dealer  in  laboratory  supplies. 

Magnets.  The  name  "magnet"  is  used  for  any- 
thing that  will  attract  iron.  Magnetite  is  a  natural 
magnet.  Pieces  of  iron  and  steel  may  be  changed  into 


The  Mariner's  Compass  303 

artificial  magnets   by   stroking   them  with  a  natural 

magnet,  and,  as  we  shall  see  in  the  next  chapter,  much 

stronger     magnets     may     be 

made  by  passing  an  electric 

current    around    a    piece    of 

steel. 

Exercise  2.  First,  try  to  see 
whether  your  knife  blade  will 
attract  small  tacks  or  other 
pieces  of  iron.  Then  draw  it 
several  times,  in  the  same  direc- 
tion, over  a  piece  of  magnetite  and 
repeat  the  trial  with  the  tacks. 

Some  magnets  are  straight 
and  are  known  as  bar  mag- 
nets (Fig.  185).  Some  are  U-shaped  and  are  called 
horseshoe  magnets  (Fig.  186).  The  needle  of  a  com- 
pass is  a  light  bar  magnet.  A  convenient  form  of  a 
magnetic  needle  for  laboratory  use  is  shown  in  Figure 


Exercise  3.  Take  the  needle  from  its  support,  hold  it 
in  your  hand,  and  present  either  end  to  some  iron  filings  or 
tacks.  Does  either  end  of  the  needle  attract  iron?  The 
same  experiment  may  be  performed  with  a  bar  magnet. 

Place  the  needle  back  on  its  support  and  bring  a  piece  of 
iron  near  either  end.  Does  the  iron  also  attract  the  needle 
at  both  ends?  A  bar  magnet,  suspended  as  shown  in  Fig- 
ure 190,  may  be  used  in  this  experiment  if  a  suitable  compass 
needle  is  not  at  hand. 

This  experiment  shows  that  a  magnet  not  only  at- 
tracts iron,  but  is  also  attracted  by  iron, 


304 


Science  for  Beginners 


FIG.  1 88.    The   iron    filings    are    attracted 
most  strongly  by  the  poles  of  the  magnet. 


The  poles  of  a  mag- 
net. The  ends  of  a 
magnet  are  called  its 
poles.  One  of  these 
poles  is  called  the  posi- 
tive or  north  pole,  and 
the  other  the  negative 
or  south  pole. 

Exercise  4.  Lay  a 
bar  magnet  in  some  iron 

filings.     What  part  of  the  magnet  attracts  the  filings  most 

strongly  ? 

The  force  by  which  the  iron  is  drawn  to  the  magnet  is 
known  as  magnetic  force.  In  Exercise  3  we  proved  that 
this  force  not  only  draws  the  iron  to  the  magnet  but  also 
draws  the  magnet  to  the  iron. 

Exercise  5.  Lay  a  piece  of  stiff  paper  over  the  magnet 
and  sprinkle  iron  filings  on  the  paper.  The  iron  does  not 
touch  the  magnet,  but  it  is  affected  by  it  because  it  has 
come  into  the  magnetic  field.  Notice  that  the  filings  tend 
to  collect  in  lines. 

The  lines  along  which  the  filings  tend  to  arrange 
themselves  are  called  lines  of  magnetic  intensity. 

Induction.  Induction  is  the  process  of  producing 
or  developing  magnetism  in  a  piece  of  iron  or  steel  by 
bringing  it  near  a  magnet. 

Exercise  6.  Magnetize  a  knitting  needle  by  drawing  it 
across  the  pole  of  a  bar  magnet.  Place  the  magnetized 
needle  upon  a  small  cork  which  is  floating  upon  the  water, 
pr  better,  suspend  it  in  the  air  by  a  small  loop  of  paper  and 


The  Mariner's  Compass  305 


string  in  such  a  way  that 
it  will  be  free  to  move. 
Notice  whether  the  needle 
tends  to  point  in  any  par- 
ticular direction  as  it 
comes  to  rest. 

The    needle   is   mag- 
netized    by     induction 

.  FIG.  189.     The  iron  filings  arrange  them- 

When    it    IS     Stroked    On       selves  along  the  lines  of  magnetic  force. 

the  magnet,  and,  like  the 

needle  of  a  compass,  points  approximately  north  and 
south.  A  needle  of  this  kind  can  be  used  to  perform 
Exercise  3 . 

Exercise  7.  With  a  bar  magnet  pick  up  a  nail.  Present 
the  outer  end  of  the  nail  to  the  end  of  another  nail,  repeat- 
ing this  several  times,  This  is  an  illustration  of  what  is 
called  magnetic  induction.  The  nail  becomes  a  magnet 
when  it  is  brought  near  the  magnet  and  it  is  then  able  to 
magnetize  and  attract  another  nail. 

It  is  an  interesting  fact  that  in  magnetizing  other 
pieces  of  iron  a  magnet  does  not  lose  any  of  its  mag- 
netism but  rather  gains  more  by  the  exercise. 

The  effect  of  one  magnet  on  another  magnet.  We 
have  found  that  either  end  of  a  magnet  will  attract 
unmagnetized  iron.  What  effect  does  one  magnet  have 
on  another? 

Exercise  8.  Present  to  either  end  of  a  magnetic  needle 
(Fig.  187)  or  of  a  suspended  bar  magnet  (Fig.  190)  the  north 
and  south  poles  of  a  second  bar  magnet.  What  results  do 
you  get? 


306 


Science  for  Beginners 


FIG.  190. 


By  this  experiment  it  is  easy  to  discover  the  impor- 
tant law  that  like  poles  repel  and  unlike  poles  attract 

each  other.  With  a  "dip- 
ping  needle"  and  a  long  bar 
magnet,  the  same  law  can  be 
proved  in  another  way  (Fig. 
191).  If  the  needle  is  moved 
toward  the  north  pole  of  the 
magnet,  the  south  pole  of 
the  needle  will  be  drawn 
down  toward  the  magnet,  and 
when  the  needle  reaches  the 
north  pole  of  the  magnet  it 
will  stand  in  a  perpendicular 
position.  The  reverse  action  will  be  produced  by  mov- 
ing the  needle  toward  the  south  pole  of  the  magnet. 

Why  the  compass  points  north  and  south.  When  a 
dipping  needle  is  carried  from  the  equator  to  the  poles 
of  the  earth,  the  needle  behaves  exactly  as  it  does  when 
it  is  moved  along  a  magnet.  As  the  journey  to  the 
north  is  made,  the  end  of  the  needle  which  points  north 
turns  more  and  more  downward,  and  if  the  needle  is 
moved  southward  exactly  the  opposite  movement 
follows.  Hence  it  is  inferred  that  the  earth  is  itself  a 
great  magnet,  having  its  positive  and  its  negative  pole. 
The  north,  or  negative,  magnetic  pole  is  northwest  of 
Hudson  Bay,  about  20  degrees  south  of  the  geographical 
north  pole.  The  south,  or  positive,  magnetic  pole  of 
the  earth  is  a  point  in  the  Antarctic  Ocean  at  the  end  of 
a  diameter  drawn  from  the  north  magnetic  pole  through 


The  Mariner's  Compass  307 

the  center  of  the  earth.     The  ordinary  magnetic  needle, 
when  it  is  permitted  to  swing  freely,  obeys  the  attrac- 


FiG.  191.    Unlike  poles  attract,  and  like  poles  repel. 

tion  of  the  earth's  magnetic  poles,  and  all  such  magnets 
point  to  these  poles.  If  a  needle  is  located  anywhere 
on  the  meridian  of  longitude  passing  through  both  the 
north  pole  of  the  earth  and  the  north  magnetic  pole, 
it  will  point  due  north  and  south.  This  is  the  line  which 
is  called  the  line  of  no  variation.  It  passes  through 
central  Ohio.  At  all  places  east  of  this  line  the  needle 
points  somewhat  west  of  north ;  at  places  west  of  it,  the 
needle  points  east  of  north. 

Other  uses  of  magnetism.  The  account  of  the  mari- 
ner's compass  and  how  it  points  the  way  across  the 
trackless  ocean  or  through  the  untraveled  forest  has 
shown  us  one  great  use  of  the  magnet;  but  it  has  not 
brought  to  light  a  vastly  greater  service  which  the 
magnet  renders.  Without  that  form  of  magnet  known 
as  the  electro-magnet,  much  of  the  work  of  the  world 
could  not  be  done.  By  its  power  we  move  railroad 
trains,  street  cars,  and  automobiles,  set  electric  fans 
to  whirling,  and  drive  the  wheels  of  great  factories. 
How  this  is  done  will  be  explained  in  the  next  chapters. 


CHAPTER  THIRTY-ONE 

ELECTRICITY 


Great  Western  Power  Company  of  California 

FIG.  192.  The  Las  Plumas  hydroelectric  plant  on  the  north  fork  of  the  Feather 
River.  The  water  is  carried  through  a  tunnel  in  the  mountains  and  falls  465 
feet  through  pipes  leading  down  the  mountain  side  to  the  power  plant  below. 
The  capacity  of  the  plant  is  100,000  horse  power,  and  the  United  States  Govern- 
ment reports  estimate  that  550,000  horse  power  could  be  generated  by  the  waters 
of  this  river. 

THE  Feather  River  rises  in  the  high  peaks  of  the 
Sierra  Nevada  Mountains  in  northern  California  and 
dashes  down  the  western  slopes  of  these  mountains 
on  its  journey  to  the  sea.  The  waters  from  the  melting 
snow  develop  an  enormous  force  as  they  plunge  over 
huge  bowlders  and  roar  through  narrow  gorges  to  the 
valley  far  below.  In  ages  past,  this  river  washed  from 
the  rocks  of  the  mountains  large  amounts  of  gold,  which 
were  found  by  the  miners  in  the  sands  of  its  lower 
courses.  Now  its  waters  are  performing  a  work  much 
more  important  to  mankind. 

On  one  side  of  the  north  fork  of  the  river  stands  a 

308 


Electricity  309 

hydroelectric*  plant.  To  this  plant  the  water  falls 
465  feet,  and  by  its  giant  power  it  sets  in  motion  the 
wheels  of  great  dynamos.  From  the  dynamos  comes 
a  wonderful  something  called  electricity,  which  is  carried 
by  wires  hung  on  steel  towers  or  through  submarine 
cables  to  many  towns  and  cities,  even  to  San  Francisco, 
1 60  miles  away. 

What  is  electricity?  How  can  the  falling  waters  of 
a  river  produce  a  stream  of  power  that  operates  rail- 
roads, gold  dredges,  and  mines,  turns  the  wheels  of 
factories,  and  lights  houses  and  towns?  What  is  the 
nature  of  this  silent  servant  of  mankind  that  cooks 
our  food,  rings  our  doorbells,  explodes  the  gasoline  in 
our  automobiles,  reproduces  the  human  voice  at  the 
farther  end  of  a  slender  wire  which  stretches  across  a 
continent,  or  projects  a  message  through  space  across 
the  vast  expanse  of  an  ocean?  We  live  in  the  age 
of  electricity.  Let  us  see  if  we  can  learn  something  of 
it  and  of  how  it  can  be  controlled. 

Early  history  of  electricity.  Thales  of  Miletus,*  one 
of  the  seven  wise  men  of  Greece,  discovered  that 
when  amber*  is  rubbed  with  silk  it  gains  the  power  to 
attract  to  itself  light  substances,  such  as  bits  of  paper 
and  fibers  of  cotton.  The  Greek  word  for  amber  is 
elektron,  and  from  this  our  word  electricity  is  derived. 

The  discovery  of  Thales  did  not  produce  any  practi- 
cal results  for  the  world  except  to  give  us  an  interesting 
fact  and  a  name.  More  than  two  thousand  years 
passed  by  before  any  advance  in  the  understanding  of 
electricity  was  made.  At  last,  toward  the  end  of  the 


310  Science  for  Beginners 

sixteenth  century,  Dr.  Gilbert,  a  physician*  to  Queen 
Elizabeth,  showed  that  the  property  which  Thales  had 
discovered  amber  to  possess  was  not  a  property  of  that 
substance  alone  but  was  also  to  be  found  in  wax,  glass, 
sulfur,  and  many  or  all  other  bodies.  We  may  repeat 
some  of  his  experiments. 

Exercise  i.  Rub  a  stick  of  sealing  wax  with  a  flannel 
cloth  and  hold  the  wax  near  small  shreds  of  paper,  cotton, 
or  lint.  Bring  the  knuckles  of  the  hand  near  the  wax.  A 
crackling  sound  may  be  heard,  and  if  the  experiment  is 
performed  in  the  dark,  a  small  bright  spark  may  sometimes 
be  seen  leaping  across  the  space  between  the  hand  and  the 
sealing  wax. 

Repeat  this  experiment,  using  a  dry  glass  tube.  A  long, 
narrow  lamp  chimney  will  do  if  no  other  glass  tube  is  at 
hand.  Rub  the  glass  with  silk. 

Exercise  2.  Draw  a  piece  of  dry,  warm  wrapping  paper 
quickly  several  times  between  the  dry  thumb  and  fingers,  or 
under  the  arm.  Then  see  if  the  paper  will  cling  to  the  wall 
of  the  room. 

Repeat  experiments  like  the  above  with  a  variety  of  sub- 
stances. For  example,  rub  with  the  hand  the  back  of  a 
cat  or  dog  that  has  become  dry  and  warm  by  lying  close  to 
the  fire;  comb  the  hair  with  a  rubber  comb;  or  scuff  the 
dry  feet  over  a  warm,  dry  rug,  and  then  hold  the  hand  near 
the  gas. 

In  all  these  experiments  electricity  is  produced  by 
friction.  When  glass,  sealing  wax,  woolen  or  silk  cloth, 
or  other  bodies  are  thus  excited,  they  are  said  to  be 
electrified,  or  charged.  The  electricity  on  such  a  body 
is  known  as  static  electricity. 


Electricity 


An  interesting  experiment. 

Many  interesting  experi- 
ments can  be  done  with 
electrically  charged  bodies. 
We  shall  begin  with  one 
that  shows  how  such  a  body 
can  exert  a  force  upon 
another  body,  without  touch- 
ing it. 

.  Exercise  3.  Balance  upon 
an  egg  placed  in  the  top  of  an 
egg  cup  a  ruler  or  a  light, 
smooth  lath  3  feet  long  or  more. 
Rub  a  glass  rod  or  a  stick  of 


FIG.  193.    Like  kinds  of  electricity 
repel  each  other. 


sealing  wax  as  before  and  present  the  electrified  end  to  the 
end  of  the  lath  or  ruler,  but  without  touching  it.  The  lath 
can  be  made  to  revolve  on  the  egg.  What  happens  when 
the  excited  rod  is  allowed  to  touch  the  lath? 

Why  does  the  excited  rod  drive  the  lath  about? 
Here  is  a  most  interesting  question  for  us  to 
answer. 

Two  kinds  of  electricity.  There  are  two  kinds  of 
electricity,  positive  and  negative,  just  as  there  are  posi- 
tive and  negative  poles  of  a  magnet.  The  charge  of 
electricity  upon  the  excited  glass  that  has  been  rubbed 
with  silk  is  said  to  be  positive,  and  that  upon  the  seal- 
ing wax  that  has  been  rubbed  with  flannel  is  called 
negative. 

Exercise  4.  (i)  Suspend  by  a  silk  string  a  glass  rod 
which  has  been  rubbed  with  silk.  Bring  one  end  of  another 


312 


Science  for  Beginners 


FIG.  194.    The  pith  ball  is  first  attracted 
to  the  excited  glass  rod  and  then  repelled. 


electrified  glass  rod  near 
the  end  of  the  one  sus- 
pended. The  latter  is 
repelled. 

(2)  In  the  same  way, 
suspend  a  stick  of  sealing 
wax  which  has  been  elec- 
trified by  rubbing  it  with 
a  woolen  cloth,  and  bring 
near  it  the  end  of  an- 
other electrified  stick  of. 

sealing  wax.     The  suspended  stick  is  repelled  as  before. 
(3)  Now  bring  an  electrified  stick  of  sealing  wax  near  to  the 

suspended  electrified  glass  rod.     These  will  attract  each  other. 

You  are  now  ready  to  announce  an  important  law; 
namely,  like  kinds  of  electricity  repel  and  unlike  kinds 
attract  each  other.  Go  back  over  your  experiments 
and  see  that  this  is  so. 

How  to  detect  electricity.  Electricity  can  be  easily 
detected  by  the  use  of  an  instrument  known  as  an 
electroscope.  A  simple  electroscope  is  shown  in  Fig- 
ure 194.  It  is  made  by  bending  a  glass  tube  or  rod, 
supporting  it  in  the  cork  of  a  bottle,  and  attaching  to 
the  rod  with  a  silk  thread  a  small  ball  made  of  pith 
from  the  inside  of  a  dry  cornstalk.  Make  at  least  two 
electroscopes  of  this  kind. 

Exercise  5.  (i)  Rub  a  dry  glass  tube  or  rod  with  silk 
and  present  it  to  the  pith  ball.  Two  things  will  happen  to 
the  pith  ball :  at  first  it  will  be  attracted ;  but  presently  the 
ball  will  fly  away,  and  then  the  excited  glass  will  repel  the 
ball. 


Electricity  313 

• 

(2)  Repeat  the  same  test  with  the  sealing  wax  rubbed 
with  the  flannel.  The  pith  ball  is  affected  in  exactly  the 
same  way. 

The  excited  glass  or  wax  causes  the  ball  to  become 
charged  with  electricity,  and  then  the  ball  is  repelled 
by  the  rod  or  wax.  As  a  magnet  will  cause  a  nail  or 
other  piece  of  iron  that  is  brought  into  contact  with 
it  to  become  magnetic,  so  a  body  that  is  electrically 
excited  will  electrify  a  second  body  that  is  brought 
near  it. 

The  effect  of  negative  and  positive  charges  of  elec- 
tricity on  each  other.  An  important  fact  about  electricity 
is  that  positive  and  negative  charges  will  neutralize,  or 
destroy,  each  other  if  they  are  brought  together. 

Exercise  6.  Electrify  two  pith  balls  by  touching  one  with 
an  excited  glass  rod  and  the  other  with  an  electrified  piece  of 
wax.  Then  set  the  electroscopes  so  that  the  balls  will  be 
near  each  other.  They  will  attract  each  other  and  come 
together.  Do  they  lose  their  electric  charges  and  fall  apart 
after  they  touch  each  other? 

When  two  bodies  heavily  charged  with  opposite 
kinds  of  electricity  are  brought  near  each  other,  the 
electricity  may  leap  from  one  to  the  other  through  the 
air.  Perhaps  you  may  have  noticed  an  electric  spark  in 
some  of  the  experiments  you  have  performed. 

Lightning.  A  stroke  of  lightning  is  a  charge  of 
electricity  which  passes  with  terrific  force  from  one 
cloud  to  another,  or  from  a  cloud  to  the  earth,  or  from 
the  earth  to  a  cloud.  The  earth  is  charged  with  one 
kind  of  electricity  and  the  cloud  with  the  other  kind, 


Science  for  Beginners 


and  the  lightning  flash 
is  a  great  electric  spark 
leaping  across  between 
the  two.  No  review 
of  the  electrical  dis- 
coveries that  have  led 
to  this  remarkable  age 
would  be  complete 
without  mention  of  the 
man  who  proved  that 
the  lightning  bolt  and 
the  electricity  that  we 
produce  by  rubbing  a 
glass  rod  with  a  piece 
of  silk  are  identical. 

Benjamin  Franklin. 
This  celebrated  man 
was  not  a  scientist  by 
profession,  but  a  states- 
man* and  writer.  His  mind,  however,  was  always  open 
to  everything  that  could  possibly  add  to  the  knowl- 
edge of  the  world.  Being  in  Boston  in  1746,  he  saw, 
for  the  first  time,  some  experiments  in  electricity,  and 
he  was  led  to  study  the  subject  carefully.  It  occurred 
to  him  that  the  lightning  of  the  clouds  and  the  elec- 
tricity that  he  had  seen  in  the  experiments  were  the 
same,  and  he  planned  an  experiment  to  prove  whether 
or  not  his  ideas  were  correct.  By  the  simple  method 
of  sending  a  silk  kite  with  small  metal  points  pro- 
jecting from  it  high  up  toward  the  clouds  in  the 


FIG.  195.  A  great  electric  spark  leaping 
across  the  space  between  a  cloud  and  the 
earth. 


Electricity  315 

midst  of  a  "thunder,"  or  electrical,  storm,  he  brought 
the  electricity  down  from  the  clouds  along  the  wet 
string  of  the  kite.  He  caught  a  heavy  charge  of 
electricity  in  a  bottle  covered  within  and  without 
with  tinfoil,  and  by  further  experiments  proved 
that  this  electricity  was  the  same  as  that  produced  by 
friction.1 

Electricity  from  chemical  action.  Volta,  an  Italian 
physicist  who  lived  from  1745  to  1827,  discovered  that 
electricity  may  be  produced  by  chemical  action.  This 
can  be  proved  by  a  few  experiments  that  are  quite  easily 
made. 

Exercise  7.  Fill  a  tumbler  or  beaker  glass  two  thirds 
full  of  water  and  add  a  small  amount  of  pure  sulfuric 
acid.  Immerse  a  strip  of  zinc  in  the  liquid  and  notice 
the  bubbles  of  gas  which  very  quickly  rise  from  the  sur- 
face of  the  zinc.  If  a  burning  match  be  brought  to  the 
gas  as  it  escapes  from  the  surface  of  the  liquid,  a  slight  ex- 
plosion will  follow.  This  will  show  that  hydrogen  is  being 
produced. 

Exercise  8.  Take  the  strip  of  zinc  from  the  bath  of  sul- 
furic acid  and,  without  drying  or  cleaning  it,  rub  a  few  drops 
of  mercury  into  it  with  a  cloth.  The  surface  will  be  coated 
over  by  a  bright  zinc-mercury  amalgam.  Place  this  amal- 
gamated zinc  back  in  the  dilute  sulfuric  acid.  Notice  that 
little  or  no  hydrogen  is  now  given  off. 

Exercise  9.     Remove  the  zinc  and  place  a  strip  of  copper 

1  The  pupil  will  find  further  information  about  how  a  glass  vessel  is 
prepared  to  make  it  hold  a  charge  of  electricity  in  any  text  on  physics 
in  the  discussion  of  the  Leyden  jar.  However,  no  pupil  should  try  to 
repeat  Franklin's  experiment.  A  Russian  scientist  lost  his  life  by 
attempting  to  do  so. 


316 


Science  for  Beginners 


or  platinum  in  the  dilute  sulfuric  acid.  No  perceptible  chem- 
ical action  will  be  noticed ;  no  hydrogen  will  be  given  off. 

Exercise  10.  Now  place 
both  the  amalgamated  zinc 
and  the  copper  in  the  liquid 
and  either  allow  the  two 
pieces  of  metal  to  touch  each 
other  at  the  top  or  connect 
them  by  a  wire  from  each. 
There  will  be  a  quick  evolu- 
tion* of  gas.  Notice  that 
the  gas  is  now  coming  from 
the  copper  and  not  from  the 
zinc. 

Now  consider  carefully 
the  results  of  these  experi- 
ments. Which  of  the  two 
metals  produced  hydrogen 

when  placed  alone  in  the  liquid  ?  Which  metal  did  not 
liberate  hydrogen  when  placed  alone  in  the  acid?  Re- 
call the  fact  that  it  is  only  when  the  two  metals  are 
joined  that  hydrogen  is  evolved,  and  that  then  the  hydro- 
gen  comes  from  the  copper  and  not  from  the  zinc.  May 
we  not  conclude  that  bringing  the  metals  together 
caused  the  hydrogen  to  be  carried  from  the  surface  of 
the  zinc  to  the  surface  of  the  copper,  where  it  escaped 
into  the  air? 

The  voltaic  cell.  A  piece  of  apparatus  like  the  one 
we  have  arranged  for  our  experiments  is  called  a  vol- 
taic  cell.  By  the  chemical  reaction  within  the  cell,  elec- 
tricity is  produced,  and  we  speak  of  a  current  of  elec- 


andH0 


FIG.  196.  When  the  wires  are  brought 
into  contact,  hydrogen  is  given  off  from 
the  copper. 


Electricity  317 

tricity  which  passes  through  the  liquid  and  carries  the 
hydrogen  from  the  zinc  to  the  copper.  The  current 
passes  from  the  copper  into  the  connecting  wires  back  to 
the  zinc,  thus  forming  a  circuit.  Joining  the  wires  and 
thus  connecting  the  two  metals  is  called  closing  the 
circuit ;  separating  them  is  breaking  the  circuit.  Notice 
that  these  experiments  have  not  furnished  any  proof  that 
a  current  does  actually  flow,  but  it  is  plain  to  be  seen  that 
in  this  case  chemical  action  has  produced  electricity,  and 
it  is  convenient  to  speak  of  a  current  in  the  circuit. 

Figure  196  shows  a  simple  form  of  the  voltaic  cell. 
Any  liquid  that  will  act  on  the  other  two  substances  may 
be  used  in  it;  the  one  essential  condition  is  that  the 
chemical  action  of  the  liquid  shall  be  greater  on  one  of 
the  substances  than  on  the  other.  It  will  be  seen  that 
there  is  a  wide  range  of  substances  that  may  be  used  for 
the  construction  of  a  voltaic  cell,  and  many  varieties  of 
these  cells  have  been  made.  A  brief  description  of 
three  forms  of  cells  that  are  commonly  used  will  be 
given  to  illustrate  some  of  the  different  materials  that 
may  be  used. 

The  gravity  cell.  This  form  (see  Figure  197)  is 
extensively  used  by  the  Western  Union  and  other 
telegraph  companies.  Crystals  of  copper  sulfate  are 
placed  in  the  bottom  of  the  battery  jar,  which  is  then 
filled  with  water.  A  piece  of  copper  is  placed  in  the 
bottom  of  the  cell,  and  a  piece  of  zinc  is  suspended  at  the 
top.  A  few  drops  of  sulfuric  acid  are  added  to  the 
water.  Both  zinc  and  copper  have  wires  leading  from 
them  out  of  the  liquid, 


Science  for  Beginners 


FIG.  197.     Some  common  forms  of  electric  cells.    No.  i  is  the  Grenet  cell, 
No.  2  is  the  gravity  cell,  and  No.  3  the  dry  cell. 

The  Grenet  cell.  In  this  form  strips  of  carbon  and 
zinc  are  suspended  in  a  solution  of  sodium  dichromate 
and  sulfuric  acid.  This  combination  furnishes  a  very 
energetic  current  for  a  short  time  and  is  much  used  for 
experimental  work  in  schools.  To  stop  the  action  of  the 
chemicals  on  the  zinc  it  should  always  be  lifted  out  of 
the  liquid  after  use.  A  good  formula  for  the  solution  for 
this  cell  is:  30  parts  sodium  dichromate,  100  parts  of 
water,  and  23  parts  of  sulfuric  acid,  all  by  weight. 

The  dry  cell.  Dry  cells  are  more  extensively  used 
than  any  other  form,  because  of  their  low  cost.  They 
are  not  actually  "dry"  cells,  as  their  name  indicates. 
The  zinc  electrode*  forms  the  outer  wall  of  the  cell,  and 
within  this  is  the  positive  electrode  of  carbon.  §ur- 


Electricity 


FIG.  198.    Electroplating. 


rounding,  the  carbon  is 
a  moist  paste  consist- 
ing of  a  mixture  of  am- 
monium chlorid,  zinc 
chlorid,  zinc  oxid,  and 
plaster  of  Paris.  The 
current  is  produced  by 
the  action  of  the  am- 
monium chlorid  upon 
the  zinc.  When  the 
cell  is  new,  it  gives  a 
strong  current. 

Terms  used  in  con- 
nection with  the  electric  cell.  The  solution  used  in 
an  electric  cell  is  called  the  electrolyte.  The  two 
metals,  or  the  metal  and  carbon,  used  to  produce  the 
current  are  the  electrodes.  The  electrode  that  is  charged 
with  positive  electricity  is  called  the  positive  electrode, 
or  positive  pole.  The  one  that  is  negatively  charged  is 
the  negative  electrode,  or  negative  pole.  The  copper  or 
carbon  is  the  positive  electrode,  and  the  zinc  is  the  neg- 
ative electrode.  A  battery  may  be  a  single  electric 
cell,  or  it  may  be  composed  of  a  number  of  connected 
cells. 

Electroplating.  Many  industrial  and  commercial  uses 
are  made  of  the  electric  current,  and  an  interesting 
example  of  such  a  use  is  found  in  the  process  of  electro- 
plating. This  is  the  process  of  depositing  a  thin  coat- 
ing of  one  metal  upon  the  surface  of  another  metal  by 
the  use  of  the  electric  current.  Brass  or  iron,  for  ex- 


320  Science  for  Beginners 

ample,  can  be  coated  with  nickel ;  or  brass  may  be  coated 
with  gold  or  silver,  as  is  done  in  the  manufacture  of 
cheap  jewelry.  The  principle  upon  which  this  process 
depends  may  be  understood  from  the  following  exer- 
cise: 

Exercise  n.  Attach  to  the  two  wires  from  an  electric 
cell  or  battery  two  strips  of  lead  or  two  silver  coins  for 
electrodes  and  place  them  in  a  solution  of  copper  sulfate. 
After  a  little  time  it  will  be  found  that  the  negative  elec- 
trode (the  one  connected  with  the  zinc  plate  of  the  battery) 
will  be  coated  with  a  thin  layer  of  copper.  The  thickness  of 
this  layer  will  depend  upon  the  time  the  process  is  allowed 
to  continue. 

If  the  solution  in  which  the  electrodes  are  immersed 
is  a  salt  of  silver,  that  metal  will  be  deposited  upon  the 
negative  electrode.  In  the  same  way,  gold  plating  can 
be  done  by  using  a  solution  of  gold  in  the  "bath." 

Conductors  and  insulators.  A  substance  which  per- 
mits electricity  to  pass  through  it  easily  is  said  to  be 
a  good  conductor ;  a  substance  through  which  electricity 
passes  with  great  difficulty  is  a  bad  conductor  and  is 
called  an  insulator.  Copper  is  one  of  the  best  conduc- 
tors known,  and  glass  is  one  of  the  best  insulators.  If 
an  electric  current  is  to  be  brought  from  the  central 
telephone  office  to  your  home,  an  iron  or  copper  wire  is 
used,  while  to  prevent  the  current  from  passing  from  the 
wire  to  the  poles  on  which  the  wire  is  hung,  a  glass  insu- 
lator is  used.  When  you  go  home  today,  be  sure  to 
notice  this  arrangement  of  telephone  and  telegraph 
wires, 


Electricity  321 

Among  good  electrical  conductors  may  be  mentioned 
metals,  charcoal,  minerals,  acids,  impure  water,  vege- 
tables, animals,  linen,  cotton.  A  list  of  good  insulators 
would  include  dry  air,  shellac,  amber,  sulfur,  wax,  glass, 
silk,  dry  paper,  rubber.*  Which  of  these  materials  are 
used  to  cover  electric  wires  ? 

Would  it  be  wise  to  sit  by  an  open  window  or  stand 
in  a  doorway  during  a  thunder  shower  when  the  wind  was 
blowing  the  damp  air  into  the  house?  Would  you 
lean  against  a  tree  if  you  were  standing  under  it  during 
a  thunder  shower?  Why  cannot  experiments  with  fric- 
tional  electricity  be  conducted  successfully  unless  the 
air  be  dry  ? 

Resistance.  There  is  no  absolutely  perfect  conduc- 
tor of  electricity.  All  substances  offer  some  resistance  to 
the  passage  of  the  electric  current,  some  more  and  some 
less.  Wherever  the  electrical  current  finds  resistance, 
heat  is  produced ;  for  example,  if  a  short  piece  of  fine 
iron  wire  is  made  a  part  of  the  circuit  of  a  voltaic  bat- 
tery7  the  wire  will  become  heated,  perhaps  enough  to 
melt  it.  Try  this  experiment. 

The  incandescent  lamp.  We  may  conduct  a  powerful 
current  of  electricity  into  houses  with  perfect  safety, 
provided  it  is  brought  into  the  house  over  a  thor- 
oughly insulated  copper  wire.  We  can  bring  it  to  any 
point  in  a  room  that  we  may  desire,  —  to  the  middle 
of  the  ceiling  or  over  the  study  table.  If  then  ;we 
cause  the  current  to  pass  through  a  substance  of  high 
resistance,  such  as  the  fine  wire  of  an  incandescent 
bulb,  intense  heat  and  light  will  be  produced.  This  is 


322 


Science  for  Beginners 


illustrated  in  an  incan- 
descent electric  light. 
You  have  noticed  how 
very  bright  the  slender 
filament  or  thread  in 
such  a  lamp  becomes. 
What  is  the  Mazda 
lamp?  Find  your  an- 
swer in  some  recent  work 
on  physics.  Who  is  the 
inventor  of  this  lamp? 

FIG.  199.    The  construction  of  an  electric   What    Other     important 
iron.   Heat  is  produced  by  the  current  which   inventions  has  he  made  ? 
passes  from  P  to  P.     The  layer  of  insulating 
material,  C,  keeps  the  current  from  passing         The     electric     toaster. 

into5'  Study  the  construction 

of  one  of  these  modern  household  inventions  and  make 
your  own  explanation  of  it.  Study  and  explain  the 
electric  flatiron,  the  electric  footwarmer,  and  other 
appliances  that  illustrate  the  principle  we  have  been 
studying. 


CHAPTER  THIRTY-TWO 

ELECTRICITY  (Continued) 

IN  the  last  chapter  we  learned  some  facts  about  elec- 
tricity, but  our  study  has  led  us  only  to  the  threshold  of 
this  great  subject.  We  shall  in  the  present  chapter 
learn  further  of  how  this  mysterious  "fluid"  can  be 
generated  and  controlled,  but  after  the  study  is  finished 
a.  hundred  interesting  experiments  in  electricity  and 
many  fascinating  pages  of  reading  matter  on  the  sub- 
ject will  be  left  for  the  student  who  has  the  interest  and 
the  energy  to  make  investigations  for  himself.  To 
help  you  in  any  readings  or  experiments  in  electricity 
that  you  may  undertake,  a  knowledge  of  the  important 
principles  of  the  subject  is  needed,  and  there  is  no 
better  way  to  begin  a  study  of  these  principles  than 
by  investigating  the  common  electric  bell. 

The  electric  door  bell.  Figure  200  is  a  diagram  show- 
ing how  an  electric  bell  is  arranged.  A  wire  leads 
out  from  one  electrode  of  the  battery  to  the  bell,  and 
another  wire  connects  the  bell  with  the  other  electrode, 
thus  forming  a  circuit  through  the  bell.  At  some  point 
in  the  circuit  a  push  button  is  inserted,  and  when  the 
finger  presses  on  the  button  the  bell  rings.  Let  us 
examine  the  different  parts  of  this  apparatus. 

The  wires.  First  of  all,  our  attention  is  directed  to 
the  wires.  They  are  of  iron  or  copper,  copper  being 
much  better  than  iron  because  it  is  a  better  conductor 
of  electricity.  Notice  the  insulation  of  the  wires  —  the 
covering  of  silk  or  gutta-percha,  or  of  cotton  threads 
soaked  in  melted  paraffin,  that  keeps  the  electricity  from 


324 


Science  for  Beginners 


T> 


FIG.  200. 


leaving  the  wires  and  flowing  off 
into  objects  which  the  wires  touch. 
The  insulation  is  removed  when 
the  wires  are  to  be  joined  to  those 
of  the  battery,  the  push  button, 
and  the  bell.  Why?  When  an 
electrician  is  arranging  an  electric 
circuit,  he  carefully  scrapes  the 
ends  of  the  wires  so  that  they  will 
be  clean  and  bright.  Why? 

The  push  button.  Figure  200 
shows  the  structure  of  a  push 
button.  The  current  passes  into 
the  button  at  A ,  but  from  B  to  C 
there  is  a  gap  that  the  current 
cannot  pass.  When  the  button 
is  pushed  down,  the  point  of  it 
touches  the  spring  C,  and  presses 
it  down  against  B,  and  the  gap  is 
closed.  The  current  then  flows  on 
through  the  beft  and  causes  it  to 
ring.  When  the  finger  is  removed 
from  the  button,  C  rises  so  that 
the  circuit  is  broken  again  and  the 
flow  of  the  current  is  stopped. 

The  bell.  The  current  enters 
the  bell  at  Z),  flows  in  the  direc- 
tion indicated  by  the  arrows,  and 
leaves  through  the  wire  at  7.  At  E 
the  wire  is  wrapped  in  coils  around 


Electricity  325 


two  rods  of  soft  iron,  Ft 
and  from  G  to  I  the 
current  flows  through  H, 
which  is  an  iron  spring 
to  which  is  attached 
the  stem  of  the  clapper  FlG-  201-  The  iron  becomes  magnetic 

when  a  current  passes  through  the  wire. 

of  the  bell.     When  the 

button  is  pushed  and  the  current  flows,  the  clapper 
viorates  rapidly  back  and  forth,  striking  on  the  gong 
and  causing  the  bell  to  ring. 

Why  the  bell  rings.  How  does  the  current  flowing 
through  the  bell  cause  it  to  ring?  This  is  a  some- 
what difficult  question  to  answer,  and  before  attempt- 
ing to  answer  it  we  shall  ask  you  to  perform  an  ex- 
periment. 

Exercise  i.  Wrap  a  piece  of  insulated  copper  wire  about 
a  piece  of  soft  iron.  A  bolt  or  large  nail  will  do  for  the 
piece  of  iron,  and  the  wire  should  be  given  10  or  12  turns 
about  it.  Now  connect  the  two  ends  of  the  wire  to  an 
electric  cell.  When  the  current  begins  to  flow  try  to  see  if 
the  iron  will  attract  iron  filings,  a  needle,  or  your  knife 
blade.  The  iron  has  become  magnetic.  Break  the  cir- 
cuit and  notice  that  the  iron  loses  its  magnetic  properties. 

When  the  electric  current  flows  through  the  bell,  the 
rods  of  soft  iron,  F,  become  magnetic  and  draw  to  them 
the  iron  spring,  H,  thus  causing  the  clapper  to  strike 
the  bell.  But  when  H  is  drawn  away  from  G,  a  gap  is 
made  in  the  circuit  and  the  current  ceases  to  flow.  The 
irons,  F,  then  lose  their  magnetic  property  and  the 
spring,  H,  leaves  them  and  again  makes  the  contact  at 


326 


Science  for  Beginners 


FIG.  202. 


The  needle  turns  at  right  angles 
to  the  wire. 


G.  This  again  starts  the 
current,  and  F  again 
becomes  magnetic  and 
again  causes  the  clapper 
to  strike  the  bell.  Thus 
the  process  of  making 
and  breaking  the  cir- 
cuit at  G  is  carried 
on  very  rapidly  as  long 
as  the  finger  is  kept  on 
the  push  button,  and 
the  clapper  moves  back  and  forth,  causing  the  bell  to 
ring. 

The  electromagnet.  Exercise  i  and  the  way  the 
electric  bell  is  made  to  ring  suggest  an  interesting  sub- 
ject for  study,  the  electromagnet.  A  few  experiments 
will  help  us  to  understand  how  it  is  constructed  and 
how  it  works. 

Exercise  2.  (i)  Place  a  suspended  magnetized  needle  or 
a  compass  under  or  over  and  parallel  to  an  insulated  wire 
through  which  an  electric  current  is  passing.  The  needle 
is  affected.  In  what  direction  does  it  move? 

(2)  Make  a  small  loop  in  the  wire  and  hold  it  near  the 
needle.    Is  the  needle  more  strongly  affected  than  it  was 
by  the  single  wire? 

(3)  Wrap  the  wire  around  a  stick,  making  a  coil  of  10  or 
12  turns,  as  was  done  in  Exercise  i.     Remove  the  stick  and 
pass  the  current  through  the  coil.     Test  again  and  note  how 
much  more  strongly  the  needle  is  affected. 

(4)  Pass  a  short  rod  of  soft  iron  through  the  coil,  as  in 
Exercise  i,  and  test  again. 


Electricity  327 

What  we  have  learned.  These  experiments  have 
brought  to  light  some  important  facts.  A  current  pass- 
ing through  a  wire  sets  up  a  magnetic  field  around  the 
wire.  The  wire  becomes  a  magnet,  the  strength  of 
which  depends  on  the  strength  of  the  current  flowing  in 
it.  As  long  as  the  current  is  passing  through  the  wire 
it  will  turn  the  magnetic  needle,  just  as  the  steel  magnet 
turns  it.  The  coil,  or  helix,  is  a  more  powerful  magnet 
than  a  single  wire;  its  strength  depends  on  the  num- 
ber of  turns  of  wire  and  upon  the  strength  of  the  cur- 
rent. You  have  seen  also  that  the  strength  of  the  coil 
magnet  is  greatly  increased  by  the  presence  of  the  iron 
core.  The  iron  intensifies  the  magnetic  field. 

The  coil  of  wire  with  its  iron  core  makes  what  is 
called  an  electromagnet.  By  using  a  great  many 
turns  of  wire  and  a  fairly  strong  current,  magnets  are 
produced  that  are  much  more  powerful  than  the  steel 
magnets  which  we  have  already  studied.  These  electro- 
magnets are  frequently  used  on  the  great  cranes  em- 
ployed in  steel  and  iron  mills  and  factories,  for  lifting 
heavy  pieces  of  iron  and  steel.  How  is  the  magnet 
made  to  attach  itself  to  the  bar  of  iron  or  steel  and  to 
release  it?  Electromagnets  are  also  used  for  separat- 
ing iron  from  mixtures  with  other  substances.  How 
is  the  electromagnet  used  in  a  flouring  mill  ? 

Electromagnets  are  found  in  a  great  many  electrical 
devices,  such  as  the  telegraph  sounder,  the  telephone, 
and  the  electric  bell,  which  we  have  studied.  Examine 
electrical  appliances  to  find  electromagnets  and  note 
how  they  are  used. 


328  Science  for  Beginners 

The  galvanometer.  The  galvanometer  is  an  instru- 
ment for  detecting  electric  currents  and  for  measuring 
their  strength.  Its  essential  part  is  a  compass  with  a 
coil  of  wire  wound  about  it.  If  this  instrument  is  con- 
nected with  the  two  wires  from  a  battery  or  is  introduced 
into  an  electric  circuit,  the  electricity  will  flow  through 
the  coil  of  wire  about  the  compass  and  cause  the  needle 
to  be  deflected.  The  stronger  the  current  the  greater 
will  be  the  effect  on  the  needle;  by  the  effect  on  the 
needle  the  strength  of  the  current  can  be  measured.1 

Making  electricity  do  work.  Electricity  is  made  to 
run  trolley  cars  and  automobiles,  to  turn  machines  in 
factories,  and  to  do  many  other  kinds  of  work.  This 
is  accomplished  by  the  use  of  electric  motors.  We 
cannot  explain  all  the  many  complicated  devices  that 
give  the  modern  electric  motor  its  efficiency,  but  a 
simple  experiment  will  show  the  principle  on  which  it 
works. 

Exercise  3.  Suspend  an  electromagnet,  such  as  was 
made  in  Exercise  i.  The  magnet  will  take  a  north  and 
south  direction  as  an  ordinary  magnet  does;  it  has  a  north 
and  a  south  pole.  Present  the  north  pole  of  an  ordinary 
bar  magnet  to  the  north  pole  of  the  electromagnet.  The 
electromagnet  will  be  repelled  and  will  turn  away. 

This  principle  is  used  in  the  revolving  machine  shown 
in  Figure  203.  A  fixed  and  permanent  horseshoe  mag- 

1  In  many  galvanometers  a  heavy  fixed  magnet  and  a  very  light  mov- 
able coil  are  used.  In  galvanometers  of  this  type  it  is  the  coil  and  not 
the  needle  which  moves  when  the  galvanometer  is  introduced  into  an 
electric  circuit. 


Electricity 


ELECTROMAGNET 


COMMUTATOR 
TO  BREAK  AND 
REVERSE  CURRENT 


PERMANENT 

^T  ENLARGED  PLAN 

v^^      JJ  OF  COMMUTATOR 


DRY 

CELLS 


FIG.  203.    The  dynamo  used  as  an  electric  motor. 

net  makes  the  sides  of  the  machine,  and  an  upright  shaft 
capable  of  turning  around  is  fixed  in  the  axis  of  the 
magnet.  To  this  shaft  is  fastened  at  right  angles  an 
electromagnet  made  by  wrapping  a  piece  of  soft  iron 
with  a  coil  of  insulated  copper  wire.  The  ends  of  the 
wire  of  the  coil  are  fastened  to  the  commutator.  This  is 
made  of  two  metallic  pieces  that  are  attached  to  oppo- 


330  Science  for  Beginners 

site  sides  of  the  shaft  so  that  they  do  not  touch  each 
other  and  are  insulated  from  the  shaft  (Fig.  203).  The 
current  from  a  battery  enters  the  machine  by  the  bind- 
ing posts  (A,  A)  and  passes  to  two  springs  ("  brushes  ") 
that  press  upon  the  metallic  pieces  on  the  shaft  and  so 
complete  the  circuit. 

When  the  machine  is  to  be  started,  the  electromagnet 
is  so  placed  that  poles  of  the  same  kind  face  each  other. 
Thus  the  magnets  repel  each  other,  and  the  shaft  begins 
to  revolve.  When  the  shaft  has  revolved  a  little  more 
than  one  quarter  of  the  way  round  (as  in  Figure  204), 
unlike  poles  begin  to  attract  each  other,  thus  causing  the 
shaft  to  revolve  through  another  quarter  of  the  way.  At 
this  point  each  brush  is  pressing  upon  the  opposite  side  of 
the  commutator  from  that  which  it  touched  at  first,  and 
therefore  the  direction  of  the  current  in  the  electromagnet 
is  reversed.  This  reversal  of  the  current  changes  the  poles 
of  the  magnet,  so  that  now  like  poles  of  the  two  magnets 
are  facing  each  other  as  at  the  beginning,  and  a  second 
half-rotation  is  therefore  begun  as  before. 

This  little  machine  is  a  simple  electric  motor,  and  the 
thousands  of  electric  motors  that  are  in  use  every  day 
all  operate  on  the  same  principle.  When  an  electric 
fan  whirls  about,  the  force  that  runs  it  comes  from  the 
attraction  and  repulsion  of  two  magnets  for  each  other, 
and  in  the  same  way  the  shafts  of  great  electric  motors 
are  made  to  revolve  many  hundreds  of  times  a  minute. 
By  this  method  we  are  able  to  transform  the  energy  of 
the  electric  current  into  motion,  or  mechanical  energy, 
and  by  cog  wheels,  pulleys,  and  belts  this  motion  may 


Electricity  331 

be  transferred  to  machinery  as  desired.  The  great  ad- 
vantage of  the  electric  motor  is  that  it  enables  us  to 
employ  the  power  where  we  want  it.  The  force  of  the 
waters  of  a  mountain  stream  can  be  used  to  generate 
electricity,  and  in  a  distant  city  the  electricity  can  be 
made  to  do  work. 

Producing  an  electric  current  with  a  magnet.  We 
have  seen  that  electricity  flowing  in  a  wire  creates  a 
magnetic  field  about  the  wire.  We  are  now  to  learn 
that  a  magnet  can  create  an  electric  current  in  a  wire. 

Exercise  4.  Fasten  the  two  ends  of  a  covered  wire  to  a 
galvanometer,  thus  making  a  circuit.  The  galvanometer 
shows  that  the  wire  is  carrying  no  current. 

(i)  Bring  the  wire  near  a  magnet.  A  horseshoe  magnet 
is  the  best  to  use.  Quickly  bring  the  wire  near  the  pole  of 
the  magnet.  The  galvanometer  needle  is  deflected,*  showing 
that  a  current  of  electricity  has  been  produced  in  the  wire.1 
>  (2)  Make  a  coil  of  the  wire  and  bring  it  quickly  near  the 
pole  of  the  magnet.  The  needle  is  more  strongly  affected 
than  before. 

(3)  Hold  the  coil  still  over  the  pole  of  the  magnet.     The 
needle  of  the  galvanometer  will  gradually  settle  back  to  the 
zero  point. 

(4)  Withdraw  the  coil  quickly  from  the  magnet.     The 
needle  is  deflected  again,  but  this  time  in  an  opposite  direction. 

(5)  Bring  the  coil  toward  or  take  it  away  from  the  magnet 
slowly  and  then  very  rapidly.     Notice  that  the  more  rapidly 
the  coil  is  made  to  enter  or  leave  the  magnetic  field,  the 
stronger  is  the  current  that  is  produced  in  it. 

1 A  sensitive  galvanometer  is  needed  to  detect  the  current  in  a  single 


332  Science  for  Beginners 

Here  we  have  found  a  third  way  to  produce  elec- 
tricity, by  bringing  a  wire  or  a  coil  of  wire  near  a 
magnet  and  taking  it  away  again.  The  current  pro- 
duced by  the  magnet  is  an  induced  current.  It  is  pro- 
duced only  when  the  wire  or  coil  moves,  and  its  strength 
depends  on  the  strength  of  the  magnet  and  the  rapidity 
with  which  the  movement  is  made.1 

Turn  back,  now,  and  read  again  page  304,  and  ex- 
amine Figure  188,  which  shows  the  iron  filings  arranged 
along  the  lines  of  magnetic  force.  If  a  wire  is  forced 
through  a  magnetic  field  so  as  to  cut  the  lines  of  mag- 
netic  force,  a  current  is  induced  in  the  wire.  Michael 
Faraday  first  discovered  this  fact,  and  it  was  one  of  the 
most  important  discoveries  ever  made  by  man.  It 
enabled  Faraday  himself  to  make  a  machine  that  would 
generate  electricity  when  it  was  whirled  about,  and 
from  machines  of  this  kind  come  nearly  all  the  vast 
amounts  of  electrical  energy  that  are  used  in  our  mod- 
ern life. 

The  electric  generator.  In  an  electric  generator  the 
current  is  produced  by  revolving  great  coils  of  wire 
within  the  arms  of  a  huge  magnet,  thus  making  the  coils 
cut  the  lines  of  force  in  the  magnetic  field  and  producing 
an  electric  current  that  can  be  led  off  from  the  machine. 
In  its  operation  the  generator  is  exactly  the  reverse  of 
the  electric  motor.  In  the  motor  the  electricity  is  led 

1  It  should  be  understood  that  the  same  results  can  be  produced  by 
moving  a  magnet  near  to  and  away  from  a  stationary  coil  of  wire. 
This  statement  may  be  tested  by  thrusting  a  magnet  within  a  coil  and 
withdrawing  it. 


Electricity 


333 


\VINDINC 
IRON  CORE 

SHEAVE6  FOR  BELT. 

TRANSMITTING  POWER- 

TO  KOTATE,  ELECTROMAGNET 


LAMP 
(^Resistance  in.  fifament* 


FIG.  204.     The  dynamo  used  as  an  electric  generator. 

into  the  machine.  In  the  generator  the  electricity 
comes  from  the  machine.  In  the  motor  the  electricity 
is  made  to  whirl  the  machine  about.  In  the  generator 
the  shaft  is  driven  about  by  water  power  or  other  power, 
thus  whirling  the  "drum"  through  the  magnetic  field 
and  generating  the  electricity. 

The  common  electric  generators,  such  as  are  used  for 


334  Science  for  Beginners 

producing  the  current  for  electric  lights,  are  made  in  the 
same  way  as  an  electric  motor,  but  there- are,  of  course, 
many  details  in  the  construction  of  the  machines  that 
cannot  be  described  here.  It  will  thus  be  seen  that  the 
electric  motor  and  the  electric  generator  are  the  same 
machine,  the  only  difference  in  them  being  the  way  they 
are  used.  This  machine  is  called  a  dynamo.  In  a  strict 
sense  either  a  motor  or  a  generator  is  a  dynamo,  but 
usually  a  generator  is  meant  when  the  term  " dynamo" 
is  used. 

The  importance  of  the  dynamo.  What  does  the 
word  dynamo  literally*  mean?  It  is  made  from  the 
Greek  word  dynamis,  meaning  " power."  From  this 
root  we  also  get  the  words  dynamics,*  dynamite,* 
dynamometer,*  and  dyne.*  All  these  words  suggest 
the  idea  of  power,  and  one  of  the  best  illustrations  of 
immense  power  is  found  in  the  modern  dynamo.  In 
the  construction  of  this  machine  our  knowledge  of  many 
of  the  facts  and  principles  of  magnetism  and  electricity 
is  utilized,  and  we  are  given  a  mechanism  by  which 
cheap  forms  of  power  can  be  transformed  into  electric- 
ity and  by  which  the  electricity,  after  it  has  been  led 
to  where  it  is  to  be  used,  can  be  transformed  again  into 
mechanical  power  for  a  thousand  purposes. 

It  is  probable  that  no  machine  ever  made  has  meant 
more  for  the  progress  of  man  than  the  dynamo.  Until  re- 
cently nearly  all  the  water  power  of  our  country  went  to 
waste,  and  even  yet  much  of  it  is  not  being  used  in  the 
work  of  man.  We  are  impressed  by  the  grandeur  and 
sublimity  of  Niagara,  Yosemite,  or  Kakabeka  Falls, 


Electricity  335 

but  our  minds  must  wonder  at  the  vast  number  of  horse- 
powers of  energy  that  are  every  day  lost  in  these  and 
other  falls.  By  means  of  the  dynamo  this  water  power 
can  be  transformed  into  electricity  and  made  to  turn 
the  wheels  of  manufacture  and  commerce,  thus  lighten- 
ing the  labors  of  millions  of  persons  in  our  land. 

The  wireless  telegraph.  We  cannot  here  explain 
the  details  of  how,  by  means  of  the  wireless  telegraph, 
messages  are  sent  halfway  round  the  earth,  but  it  is 
fitting  that  this  wonderful  instrument  should  be  men- 
tioned before  our  study  of  electricity  is  closed.  The 
essential  part  of  the  sending  apparatus  is  a  group  of 
long,  heavily  charged  wires  (the  antennae)  and  a  mech- 
anism for  causing  surgings  back  and  forth,  or  oscil- 
lations, of  the  electric  charge  in  the  wires.  These 
oscillations  cause  waves  to  run  out  through  the  ether, 
"just  as  a  stick  laid  on  water  and  shaken  up  and  down 
sends  out  ripples  over  the  surface  of  the  water."  By 
suitable  apparatus  these  ether  waves  are  caught  and 
the  message  is  read  perhaps  hundreds  or  even  thou- 
sands of  miles  from  the  point  where  it  was  sent. 

Ether  waves.  No  subject  in  all  science  is  more 
fascinating  than  the  ether  vibrations  which  were  men- 
tioned in  the  chapter  on  light  and  which  are  the  bearers 
of  the  telegraphic  messages  that  can  now  be  sent  so 
swiftly  and  to  such  long  distances  through  space. 
These  waves  are  everywhere  all  about  you,  —  racing  in 
great  numbers  through  your  room,  striking  against  your 
body,  running  through  space  in  a  medley  of  motion 
that  almost  passes  belief,  some  of  them  even  passing 


336  Science  for  Beginners 

through  solid  materials  like  glass  and  wood.  The 
shortest  of  these  waves  are  the  X-rays ;  the  longest  are 
the  electric  waves  used  in  wireless  telegraphy,  which 
are  many  yards  in  length.  Longer  than  the  X-rays 
are  the  waves  of  light,  which  the  eye  is  attuned  to 
receive;  longer  than  the  light  vibrations  are  the  heat 
waves,  which  in  a  former  experiment  (page  249)  you 
felt  beating  against  your  hand.  Already  it  is  possible 
to  telephone  by  means  of  ether  waves,  and  some  scien- 
tists look  forward  to  the  day  when  the  energy  that  we 
need  for  heat  and  power  and  light  will  be  sent  where  it 
is  needed  in  the  form  of  ether  waves.  About  342  mil- 
lion million  horse  power  of  energy  is  each  minute  sent 
in  this  way  to  the  earth  from  the  sun. 


CHAPTER  THIRTY-THREE 

WORK  AND  ENERGY 

THE  true  scientist  does  not  allow  himself  to  become 
so  busy  with  his  hands  that  his  mind  becomes  confused. 
There  is  no  hurry  in  his  work,  and  he  often  sits  down 
quietly,  far  from  his  laboratory,  to  think  over  the  mean- 
ing of  the  experiments  that  he  has  made.  He  does  not  try 
to  use  his  apparatus  in  as  many  different  ways  as  possible, 
nor  does  he  aimlessly  pile  up  masses  of  information  on 
many  different  subjects ;  but  he  interprets  his  work  as 
he  carries  it  on  and  thinks  over  the  conclusions  that  can 
be  drawn  from  it. 

In  this  chapter  you  will  not  be  expected  to  perform 
any  experiments,  nor  will  you  need  your  notebook  to 
record  your  observations.  We  shall  ask  you  to  be  a 
thinking  scientist;  most  of  the  chapter  will  be  a  con- 
sideration of  work  that  you  have  already  done.  The 
only  piece  of  apparatus  that  you  will  need  for  these 
lessons  will  be  your  brain,  and  it  is  hoped  that  this 
machine  will  be  in  good  condition;  for  the  greatest 
difference  between  a  good  and  a  poor  scientist  lies,  not 
in  the  hand,  but  in  the  mind. 

Work.  Whenever  a  force  acts  on  anything  to  move 
it,  change  its  motion,  or  check  its  motion,  work  is  done. 
When  you  slide  a  box  along  the  floor,  you  do  work. 
When  you  run  or  when  you  throw  a  ball,  even  though 
it  be  done  in  play,  you  are  doing  work.  When  a  bird 
flies,  when  an  automobile  moves,  or  when  the  brakes 
bring  a  moving  train  to  a  stop,  force  is  exerted  and  work 
is  accomplished.  By  work,  then,  we  mean  the  effect 

337 


338  Science  for  Beginners 

produced  by  the  force,  and  where  there  is  no  effect,  no 
work  has  been  done. 

Quantity  of  work.  If  a  teamster  is  hired  to  haul  a 
load  of  grain  to  market,  he  first  takes  note  of  the  size 
of  the  load  and  then  immediately  wants  to  know  how 
far  it  is  to  the  place  where  it  is  to  be  delivered.  His 
team  will  have  to  exert  a  certain  force  to  haul  the  load, 
and  it  also  makes  a  difference  through  what  distance 
that  force  must  act.  The  farmer  knows  that  it  requires 
twice  as  much  work  to  plow  two  acres  as  it  does  to  plow 
one.  The  horses  exert  the  same  force  on  the  plow 
while  doing  the  one  piece  of  work  as  they  do  in  the  other, 
but  they  exert  that  force  through  twice  the  space.  It 
would  require  the  same  amount  of  work  to  carry  1000 
bricks  up  a  ladder  as  to  carry  500  bricks  up  two  such 
ladders,  or  to  carry  2000  bricks  up  a  ladder  one  half  as 
high. 

The  quantity  of  work,  then,  depends  upon  two  factors, 
(i)  the  force  exerted  and  (2)  the  distance  or  space 
through  which  the  force  acts;  that  is,  the  work  done 
is  equal  to  the  force  multiplied  by  the  distance. 

Work  =  force  X  distance 

Time  and  effort  not  factors  in  work.  It  will  be  noticed 
that  in  the  laboratory  of  the  scientist  no  account  is  taken 
of  the  time  consumed  in  work.  It  takes  the  same  amount 
of  work  to  complete  a  given  task,  no  matter  whether  it 
be  done  in  ten  minutes  or  in  an  hour,  and  the  scientist 
gives  his  attention  to  the  amount  of  work  done  and  not 
to  the  time  it  takes  to  do  it. 


Work  and  Energy 


339 


Furthermore,  the  scientist  is  not  interested  in  the 
amount  of  effort  it  takes  to  do  work.  If  you  attempt 
to  lift  a  chair  on  which  you  are  sitting  you  are  not  doing 
work  at  all,  in  a  scientific  sense,  because  you  are  accom- 
plishing nothing;  and  if  you  wear  yourself  out  lifting 
at  the  corner  of  a  house,  it  is  not  work,  but  a  foolish 
waste  of  strength.  It  is  the  result  secured,  not  the  time 
and  effort  expended,  that  really  counts,  and  this  is  all 
the  scientist  takes  into  account  in  considering  how  much 
work  has  been  done. 

How  shall  we  measure  work?  We  measure  milk 
by  the  quart,  sugar  by  the  pound,  dress  goods  by  the 
yard,  land  by  the  acre,  wood  by  the  cord.  We  measure 
illuminating  gas  by  the  thousand  cubic  feet.  Coal  is 
bought  by  the  ton.  We  pay  for  cement  sidewalks  or 
paving  by  the  square  foot  or  square  yard.  We  some- 
times pay  for  city  lots  at  ten,  a  hundred,  or  a  thousand 
dollars  "  per  front  foot."  How  shall  we  measure  work? 

If  we  use  the  Eng- 
lish system,  the  unit 
of  work  is  the  foot 
pound.  This  is  the 
work  done  by  a  force 
of  i  pound  acting 
through  a  space  of  i 
foot ;  that  is,  it  is  the 
amount  of  work  re- 
quired to  lift  i  pound 

tO  a  height  Of   I  foot.       FlG;   2°5'  .  A  foot  pound  is  the  amount  of 
3  t         work  required  to  lift  i  pound  to  the  height 

How   much   work   is     of  j  foot. 


34O  Science  for  Beginners 

required  to  lift  a  brick  that  weighs  5  pounds  to  the  top 
of  a  box  that  is  3  feet  high  ? 

Power.  Sometimes  we  are  interested  in  knowing  how 
fast  a  given  piece  of  work  can  be  done  by  a  machine. 
In  this  case,  the  element  of  time  is  considered.  By 
power  is  meant  the  rate  or  speed  of  doing  work.  In 
order  to  understand  what  this  means,  let  us  study  the 
following  problem : 

To  carry  100  bricks,  each  weighing  5  pounds,  to  a 
mason  on  a  scaffold  which  is  n  feet  high  would  require 
500  X  ii  or  5500  foot  pounds  of  work,  whether  the  task 
were  performed  in  an  hour  or  a  minute.  When  we 
measure  the  work  in  this  way,  the  time  consumed  plays 
no  part ;  only  the  force  and  the  distance  are  considered. 
But  it  is  frequently  very  important  to  know  how  long 
it  will  take  to  do  the  work  or  how  fast  a  machine  can 
work.  Suppose,  then,  that  a  machine  is  used  to 'haul 
the  100  bricks  up  to  the  scaffold  and  that  it  can  do  this 
in  10  seconds.  The  machine  will  then  be  doing  work 
at  the  rate  of  550  foot  pounds  a  second.  We  could  then 
describe  this  machine  by  saying  that  it  is  able  to  do  550 
foot  pounds  of  work  every  second.  An  engineer  or  a 
mechanic  would  describe  such  a  machine  by  saying  it 
is  a  machine  of  one  horse  power. 

James  Watt,  an  Englishman  who  made  great  improve- 
ments on  the  steam  engine,  described  his  engines  in  this 
way,  for  he  thought  that  a  good  horse  was  able  to  do 
work  at  the  rate  of  550  foot  pounds  per  second  and  keep 
it  up  all  day.  The  fact  is  that  an  average  horse  can  do 
work  only  about  three  quarters  as  fast  as  this. 


Work  and  Energy  341 

A  horse  power  is  the  work  which  must  be  done  in 
order  to  lift  550  pounds  i  foot  in  i  second. 

To  compute  the  horse  power  of  an  engine,  find  the 
number  of  foot  pounds  it  can  do  in  one  second  and 
divide  this  number  by  550 : 

Horse  power  (H.P.)  =  foot  pounds  per  second 

550 

What  is  meant  by  a  lo-horse-power  engine?  How 
many  horses  would  it  take  to  do  the  work  of  such  an 
engine  ? 

How  many  pounds  will  a  loo-horse-power  engine  lift 
i  foot  in  i  minute  ? 

How  far  will  it  lift  100  pounds  in  a  minute? 

Work  done  by  machines  and  by  the  forces  of  nature. 
Let  us  remind  ourselves  that  it  is  not  alone  men  and 
boys,  women  and  girls,  horses,  oxen,  mules,  and  other 
living  things  that  are  capable  of  doing  work,  but  that 
work  on  the  grandest  scale  is  done  by  the  forces  of 
nature  and  by  hundreds  of  different  kinds  of  machines 
which  employ  a  large  number  of  different  kinds  of  force. 
Thus  we  speak  of  the  work  done  by  running  water,  the 
steam  engine,  the  dynamo,  heat,  the  sun's  rays,  the 
ocean's  waves,  and  many  other  things.  Did  you  ever 
see  the  sidewalk  pushed  up  and  broken  by  the  roots 
of  a  tree  growing  underneath?  Work  was  being  done 
in  this  case  also. 

Energy.  Another  word,  and  the  idea  for  which  it 
stands,  must  now  be  studied.  We  stand  before  Niagara 
Falls  and  think  of  the  tremendous  amount  of  energy  in 
the  great  mass  of  falling  water ;  or  we  look  upon  the 


342  Science  for  Beginners 

throbbing  locomotive  and  estimate  the  energy  by  which 
a  train  of  cars  may  be  drawn  so  rapidly  from  city  to  city. 
A  baseball  pitcher  rolls  up  his  sleeve  and  shows  the  well- 
developed  muscles,  and  we  do  not  wonder  that  his  arm 
possesses  energy  enough  to  throw  the  ball  with  such 
speed.  We  ride  upon  an  electric  car  and  wonder  where 
the  energy  is  concealed  by  which  the  car  is  moved  along 
the  tracks  so  swiftly  and  smoothly.  Think  of  the  energy 
wrapped  up  in  a  ton  of  gunpowder ;  of  the  energy  set 
loose  in  a  stroke  of  lightning,  in  the  outburst  of  a  vol- 
cano, or  in  the  heat  and  light  of  the  sun,  as  it  stirs  into 
activity  the  giant  forces  of  the  winds  and  the  waves  of 
the  sea.  Study  the  world  of  energy  about  you  and  you 
may  conclude  that  it  is  even  more  interesting  and  more 
important  to  mankind  than  is  the  world  of  matter. 

What  is  energy  ?  The  question  we  naturally  ask  first 
about  energy  is,  What  is  it  ?  This  is  a  difficult  question 
to  answer,  but  we  have  found  out  what  energy  can  do, 
and  we  say  that  energy  is  the  capacity  to  do  work.  In 
other  words,  anything  that  can  do  work  has  energy.  A 
short  review  will  show  us  that  we  have  been  studying 
energy  for  some  time. 

Different  forms  of  energy.  A  moving  hammer  drives 
the  nail  into  the  wood;  a  moving  steamship  hits  the 
wharf  with  great  force;  the  moving  plow  tears  apart 
the  earth  and  throws  the  furrow  over;  the  moving 
water  turns  the  wheel  of  the  mill ;  and  the  moving  air 
sets  the  windmill  to  spinning  about.  Anything  that  has 
motion  has  the  power  to  do  work;  it  has  mechanical 
energy,  or  the  energy  of  motion.  Turn  back  to  Chapter 


Work  and  Energy  343 

Twenty-two  and  note  that  you  have  already  studied  this 
form  of  energy. 

Heat  can  lift  water  (Exercise  2,  page  243) ;  it  can  force 
the  mercury  up  the  tube  of  the  thermometer  (Exercise 
3,  page  253) ;  it  can  melt  ice  and  drive  the  molecules 
of  water  apart  so  that  the  liquid  water  is  converted  into 
steam.  Heat  causes  mighty  winds  to  sweep  across  the 
surface  of  the  earth  and  vast  ocean  currents  to  carry 
millions  of  tons  of  water  across  the  beds  of  the  sea.  It 
is  evident  that  heat  can  do  work ;  heat  also  is  a  form  of 
energy,  and  one  that  you  have  studied. 

Turn  back  and  review  page  283.  The  light  drives 
the  little  machine  about,  breaks  down  the  molecules  of 
silver  in  the  photographic  plate,  and  builds  food  in  the 
leaves  of  plants.  Light  also  is  a  form  of  energy.  With- 
out knowing  it,  we  studied  energy  when  we  studied 
light. 

Electricity  falls  in  a  tremendous  lightning  stroke 
from  the  cloud,  shattering  the  tree  that  it  strikes ;  or 
it  flows  silently  along  a  wire,  ringing  our  doorbells  for 
us,  carrying  our  messages  by  telephone  or  telegraph, 
pulling  our  trolley  cars  and  trains,  and  driving  machinery 
of  a  hundred  different  kinds.  Electricity  also  must  have 
energy,  since  it  can  do  work  in  so  many  different  ways. 

A  charge  of  dynamite  explodes  and  a  great  mass  of 
rock  and  earth  is  hurled  high  in  the  air.  Gasoline  ex- 
plodes in  the  cylinder  of  an  automobile  engine  and  the 
heavy  machine  is  driven  along  the  street.  A  basket-ball 
player  eats  her  food  and  from  it  gets  the  strength  which 
she  uses  in  playing  the  game. 


344 


Science  for  Beginners 


The  kind  of  energy 
which  is  in  the  dyna- 
mite, gasoline,  and  food 
is  called  chemical  en- 
ergy. It  is  stored  in  the 
molecules,  and  when  the 
molecules  are  broken  up 
the  energy  is  released 
and  the  work  is  done. 
In  the  earlier  chapters 
of  this  book  we  studied 
many  examples  of 
chemical  changes  that 
released  energy  in  the 
form  of  heat  or  light. 

Motion,  heat,  light, 
electrical  energy,  and 
chemical  energy  can  all 
do  work.  They  are 
all  different  forms  of 
energy. 

Transformation 
of  energy.  One  of  the 
great  facts  about  energy 
is  that  one  form  of  energy,  can  be  transformed,*  or 
changed,  into  other  forms.  The  motion  of  the  ham- 
mer is  changed  into  the  heat  of  the  nail  (Exercise  7, 
page  247) ;  the  light  of  the  sun  is  changed  into  heat  (Ex- 
ercise 1 6,  page  251) ;  electrical  energy  can  be  changed  to 
heat,  light,  or  motion,  and  the  chemical  energy  of  our 


FIG.  206.  Chemical  energy  released.  An 
explosion  of  a  submarine  mine  containing 
100  pounds  of  guncotton. 


Work  and  Energy  345 

food  is  turned  into  the  heat  and  strength  of  our  bodies. 
Perhaps  the  story  of  some  of  the  transformations  of  en- 
ergy with  which  you  are  familiar  may  help  to  make  this 
subject  clear  to  your  mind. 

When  coal  is  burned  under  the  boiler  of  a  steam  engine, 
the  chemical  energy  of  the  coal  is  changed  to  heat,  and 
the  heat  sets  the  molecules  of  the  water  into  more  rapid 
motion  and,  pushing  them  far  apart,  produces  steam. 
The  steam  molecules  hammer  on  the  piston  of  the  engine 
and  push  it  on,  thus  producing  motion,  or  mechanical 
energy,  in  that  machine.  This  mechanical  energy  may, 
in  turn,  be  used  to  run  a  dynamo  and  thus  produce  the 
energy  of  the  electric  current.  The  electrical  energy 
can  be  carried  along  wires  to  any  distance,  and  at  any 
place  we  desire  it  may  again  be  changed  into  the  energy 
of  heat  or  light,  or  it  may  be  used  to  produce  motion  in 
all  kinds  of  machines.  So  it  is  that  constantly,  all 
around  us,  one  form  of  energy  is  being  changed  into 
another  for  the  convenience  of  man. 

But  we  have  not  yet  seen  the  most  interesting  example 
of  this  principle  of  the  transformation  of  energy.  We 
must  ask  other  questions :  Where  did  the  coal  get  its 
energy  to  give  to  the  fire,  the  steam,  the  motion  of  the 
engine  and  dynamo,  the  electricity  and  the  light?  What 
produced  the  coal? 

Coal,  as  you  know,  is  produced  from  plants.  Where 
do  plants  get  their  energy?  Think  a  moment.  Can  a 
plant  develop  and  grow  in  the  dark?  You  know  it 
cannot,  and  the  great  secret  is  out.  The  story  sounds 
like  the  story  of  "  the  house  that  Jack  built."  Here 


346  Science  for  Beginners 

it  is :  the  energy  of  the  sunlight  is  transformed  in  the 
plant  into  chemical  energy,  and  this  is  stored  up  in 
the  coal.  Then  the  energy  of  the  coal  is  turned  into 
heat  by  the  burning  of  the  coal  and  that  into  other 
forms  of  energy,  until  it  appears  in  the  light  which  comes 
from  the  electric  bulb.  We  light  our  houses  by  sun- 
shine which  fell  upon  the  earth  millions  of  years  ago. 

The  conservation  of  energy.  The  greatest  fact  that 
we  have  learned  about  energy  is  that  it  cannot  be  either 
created  or  destroyed ;  that,  like  matter,  it  can  only 
be  changed  from  one  form  to  another.  This  is  the  law 
of  the  conservation  of  energy :  When  one  form  of  energy 
is  lost,  an  equal  amount  of  energy  in  another  form  always 
appears  to  take  its  place.  Thus  when  motion  is  checked, 
heat  is  produced.  When  electrical  energy  disappears, 
heat,  light,  or  motion  appears.  When  heat  is  absorbed, 
an  increased  movement  in  the  molecules  follows;  and 
the  light  which  shines  out  into  the  darkness  is  not  lost 
but  warms  the  objects  on  which  it  falls.  We  live  in  a 
changing  world,  but  not  in  a  fleeting,  vanishing  world. 
Both  matter  and  energy  exist  on  and  on ;  when  they  seem 
to  drop  out  of  existence,  they  have  only  changed  to 
other  forms,  j 

Some  questions  about  energy.  Would  it  be  possible 
to  build  a  "  perpetual  motion  machine,"  —  a  machine 
that  would  run  on  and  on  and  give  power  to  other  machin- 
ery, without  being  provided  with  energy  from  some  out- 
side source? 

What  kind  of  energy  does  your  body  use?  What 
kind  of  energy  does  a  waterwheel  use?  What  kind  of 


Work  and  Energy  347 

energy  does  a  steam  engine  use  ?  Does  an  electric  light 
turn  all  the  energy  of  the  electricity  that  comes  to  it  into 
light  ?  Why  is  a  Mazda  lamp  more  economical  than  the 
old-fashioned  carbon-filament  electric  lamp  ?  What  ani- 
mal gives  off  "  cold  light,"  —  light  that  is  produced  with- 
out wasting  any  energy  in  heat? 

Where  do  we  go  for  energy  to  carry  on  the  world's 
work  ?  What  kind  of  energy  is  used  to  lift  the  water  to 
the  mountain  tops  ?  What  is  the  source  of  the  energy 
that  causes  the  winds  to  blow?  Where  did  the  energy 
come  from  that  is  stored  in  food? 

Active  and  stored  energy.  Energy  may  be  active, 
like  the  energy  of  the  water  that  pours  over  Niagara 
Falls,  the  light  that  beats  down  from  the  sun,  or  the 
electrical  energy  that  causes  a  motor  to  revolve.  It  may 
be  stored  up  and  inactive,  as  the  energy  in  a  reservoir  of 
water  collected  on  a  mountain  height,  a  spring  that  has 
been  tightly  wound,  or  the  chemical  energy  that  is  in  a 
piece  of  dynamite,  a  lump  of  coal,  or  a  slice  of  bread.1 

Energy  is  stored  in  the  rock  that  is  lying  high  on  the 
mountain  side.  It  becomes  active  when  the  rock  is 
loosened  from  its  resting  place  and  crashes  down  to  the 
valley  below.  By  making  a  dam  across  a  mountain 
stream  above  Johnstown,  Pennsylvania,  vast  amounts 
of  energy  were  stored  in  a  great  reservoir  of  water,  to 
be  drawn  on  as  it  was  needed  to  run  the  machinery  of 
that  busy  manufacturing  city.  By  the  bursting  of  the 
dam  this  energy  was  in  a  moment  released,  and  the 

1  Energy  in  its  active  form  is  called  kinetic  energy.  In  its  stored  or 
inactive  form  it  is  called  potential  energy. 


348 


Science  for  Beginners 


FIG.  207.      When  the  water  falls  on  the  wheel,  the  energy  stored  in  it  becomes 

active. 

active  mechanical  energy  of  the  flood  of  water  which 
rushed  madly  down  the  valley  carried  death  and  destruc- 
tion to  everything  in  its  path. 

Other  illustrations  of  stored  energy  may  be  found  in 
the  hammer  held  high  in  the  air  ready  to  strike;  the 
loaded  gun ;  the  engine  standing  still  but  with  the  steam 
hissing  hot  and  ready  to  do  its  work;  a  load  of  coal; 
a  tank  of  gasoline ;  the  charged  electric  battery ;  a  base- 
ball pitcher  "  winding  up,"  or  a  tennis  player  ready  to 
send  a  swift  serve  over  the  net. 

Some  facts  we  have  learned.  Energy  is  the  ability 
to  do  work. 

Energy  is  the  cause,  work  is  the  effect. 

Motion,  heat,  light,  electrical  energy,  and  chemical 
energy  are  different  forms  of  energy. 

One  form  of  energy  can  be  changed  into  other  forms, 
but  energy,  like  matter,  is  indestructible. 

Energy  may  be  active,  or  it  may  be  stored  in  an  inactive 
form. 


CHAPTER  THIRTY-FOUR 

AIDS  TO  OUR  WORK 


FIG.  208.    The  road  is  a  machine  which  enables  the  horses  to  lift  the  load 
gradually  to  the  top  of  the  hill. 

No  animal  except  man  ever  makes  use  of  a  machine. 
For  example,  a  mole  or  a  prairie  dog  will  burrow  in  the 
ground  in  order  to  provide  itself  with  a  place  of  shelter 
and  safety ;  a  bird  will  build  its  nest  for  a  home  out  of 
sticks  or  grass.  But  in  .neither  case  does  the  animal 
make  use  of  any  tools  except  those  with  which  nature 
has  provided  it ;  the  mole  uses  its  feet  and  claws  and  the 
bird  its  bill  and,  occasionally,  its  feet. 

A  man  might  dig  a  well  by  simply  removing  the  earth 
with  his  hands,  but  this  is  not  the  way  a  man  goes  about 
such  a  task.  In  order  to  do  the  work  more  easily,  he 
brings  to  his  aid  a  pickax  to  loosen  the  soil  and  a  shovel 
to  lift  it  out.  When  the  depth  of  the  well  becomes 
greater  than  the  length  of  the  handle  of  his  shovel,  he 
may  use  a  bucket  with  a  rope  attached  to  it  to  draw  out 


350 


Science  for  Beginners 


the  earth.  He  may  also  place  a  pulley  above  him  and, 
passing  the  rope  over  it,  make  it  possible  to  elevate  the 
bucket  of  earth  by  pulling  on  the  rope  from  the  bottom 
of  the  well.  In  some  cases  a  man  may  even  call  to  his 
aid  very  complex  well-digging  machinery  to  make  a 
hole  in  the  earth,  and  then  use  another  machine  which 
he  calls  a  pump  to  draw  the  water  from  the  well. 

What  a  machine  is.  A  machine  is  anything  that 
lightens  the  labor  of  man  or  gives  him  more  efficiency 
in  his  work.1  It  may  be  some  device  like  a  needle, 
hammer,  saw,  screw  driver,  or  crowbar  that  enables  man 
to  use  his  own  strength  to  better  advantage;  it  may 
be  something  like  a  wagon,  plow,  or  binder  that  makes 
it  possible  for  him  to  use  the  strength  of  animals  in  his 
labor;  or  a  machine  like  the  windmill,  waterwheel, 
automobile,  or  steam  engine,  that  turns  the  vast  forces 
of  nature  to  the  accomplishment  of  his  work. 
The  present  time  an  age  of  machinery.  The  pres- 
ent time,  more  than  any  other 
period  in  the  history  of  the 
world,  is  an  age  of  machinery. 


FIG.  209.    A  simple  machine  which  increases  the  lifting  power  of  man. 

1  A  tool  is  but  the  extension  of  a  man's  hand,  and  a  machine  is  but 
a  complex  tool.  And  he  that  invents  a  machine  augments  the  power  of 
a  man  and  the  well-being  of  mankind.  —  HE^RY  WARP  BEECHER, 


Aids  to  Our  Work 


FIG.  210.  A  machine  which  gives 
an  advantage  in  lifting  power  and 
in  the  direction  in  which  the  force 
is  applied. 


By  the  aid  of  machines  man  travels  over  sea  and  land 
and  flies  through  the  air.  By  the  aid  of  a  machine  man 
is  able  to  haul  immense  train- 
loads  on  railways  or  even  over 
ordinary  roads  with  no  rails  to 
run  upon.  By  other  machines 
he  sends  his  thoughts  across 
the  ocean  and  talks  with  those 
who  are  hundreds  or  even 
thousands  of  miles  away.  Very 
many  times  a  day  we  use  some 
instrument  or  tool  to  help  us 
at  even  our  simplest  tasks. 
If  you  will  carry  out  the  following  exercises  you  will 
realize  how  greatly  man's  activities  differ  from  those  of 
the  mole,  the  bird,  and  other  lower  animals. 

Exercise  i.  Begin  in  the  morning  and  make  a  list  of 
all  the  tools,  implements,  and  mechanical  devices  that 
you  use  throughout  the  day,  —  comb,  spoon,  knife,  tooth- 
pick, door  hinges,  poker,  street  car,  needle,  sewing,  ma- 
chine, baseball  bat,  and  other  things.  What  is  the  total 
number  ? 

Exercise  2.  Make  a  list  of  the  machines  that  you  see  in 
use  in  one  day  and  record  the  work  that  is  done  by  each. 
Think  what  our  lives  would  be  like  if  all  this  work  had  to 
be  done  by  hand. 

Two  advantages  in  the  use  of  machines.  A  team  of 
horses  cannot  draw  a  heavily  loaded  wagon  straight  up 
the  face  of  a  very  steep  hill.  But  if  a  road  to  the  top  of 
the  hill  be  laid  out  so  that  it  winds  back  and  forth  across 


352  Science  for  Beginners 


FIG.  211. 

the  hillside  and  rises  with  only  a  gentle  grade,  the  horses 
can  take  the  load  to  the  summit  of  the  hill. 

The  amount  of  work  required  to  lift  the  wagon  to  the 
hilltop  is  the  same  whether  it  goes  up  the  steep  hillside 
or  is  brought  up  the  more  gradually  rising  road.  For 
example,  if  the  wagon  and  its  load  weigh  3000  pounds 
and  the  hill  is  100  feet  high,  it  will  take  300,000  foot 
pounds  of  work  to  bring  the  wagon  to  the  top  (page  339). 
The  advantage  in  the  road  is  that  it  allows  the  horses 
to  lift  the  load  a  shorter  distance  for  each  foot  that  they 
travel,  —  to  wind  back  and  forth  across  the  hillside, 
lifting  the  load  little  by  little  until  they  get  it  to  the  top. 
A  greater  force  could  pull  the  wagon  along  a  short,  steep 
road  straight  up  the  hill ;  the  lesser  force  which  the 
horses  are  able  to  exert  can  do  the  same  work  if  it  is 
allowed  to  act  through  a  long  distance  and  raise  the  load 
gradually.  It  is  thus  evident  that  by  increasing  the  dis- 
tance through  which  a  force  acts,  its  power  to  move  a 
heavy  body  can  be  increased. 

Exercise  3.  Set  a  sharp-edged  block  on  the  corner  of  a 
table  and  balance  a  yardstick  across  it;  or  suspend  the 
yardstick  as  shown  in  Figure  211.  Hang  a  3-pound  weight 
6  inches  from  the  center  on  one  arm  and  a  i -pound  weight 


Aids  to  Our  Work 


353 


FIG.  212. 

on  the  end  of  the  other  arm.  The  two  weights  will 
exactly  balance  each  other.  With  a  slight  touch  of  the 
finger  to  assist  it,  the  i -pound  force  lifts  a  weight  of  3  pounds. 
It  is  clearly  seen  that  by  the  simple  machine  which  we  have 
arranged,  the  lifting  power  of  the  i -pound  force  has  been 
increased  threefold. 

Now,  remove  the  weights  and  raise  or  lower  the  long  arm 
of  the  stick  so  that  the  i -pound  weight  moves  i  foot;  at 
the  same  time  measure  the  distance  that  the  3-pound  weight 
moves.  It  will  be  found  that  the  3-pound  weight  moves 
4  inches,  exactly  -J  as  far  as  the  i-pound  weight  moves. 
We  have  found  that  a  i -pound  force  acting  through  a  space 
of  i  foot  will  lift  a  3-pound  weight  through  a  distance  of 
4  inches. 

The  purpose  of  giving  the  small  force  the  long  arm 
of  the  stick  is  to  allow  it  to  act  through  a  longer 
distance  when  the  weight  is  moved ;  for  a  small 
force  acting  through  a  long  distance  can  lift  a  heavy 
weight  through  a  short  distance.  We  see,  there- 
fore, that  one  advantage  in  using  machines  is  that  by 


354  Science  for  Beginners 


FIG.  213.    A  machine  that  gives  an  advantage  in  the  speed  with  which   the 
object  is  moved. 

means  of  them  we  can  make  forces  act  through  longer 
distances  than  the  objects  are  moved,  and  thus  magnify 
the  power  of  the  forces  to  do  heavy  work.  When  a 
man  pries  a  stone  out  of  the  ground  with  a  crowbar  (Fig. 
209),  he  greatly  increases  his  lifting  power  by  moving 
the  end  of  the  crowbar  in  his  hands  through  a  com- 
paratively long  distance  while  the  stone  is  raised  a 
much  shorter  distance.  When  we  raise  a  bucket  of 
water  with  a  windlass  (Fig.  210),  we  gain  in  lifting 
power  by  making  the  hand  move  through  a  wide  cir- 
cle while  the  rope  is  wound  up  and  the  bucket  raised 
only  a  short  distance.  The  lower  pair  of  scissors  shown 
in  Figure  216  is  used  for  cutting  tin  and  iron.  Do  you 
see  how  the  force  acts  through  a  greater  distance  than 
the  blades  move  and  that  there  is  a  gain  in  power  when 
scissors  of  this  kind  are  used?  A  "mechanical  ad- 
vantage "  is  secured  by  using  machines  of  this  kind. 
Figure  213  is  a  whirligig,  merry-go-round,  or  flying- 
jinny.  By  pushing  on  the  arm  close  to  the  center  the 


Aids  to  Our  Work 


355 


boy  on  the  ground  is  able 
in  a  revolution  to  move 
the  ends  of  the  arms  much 
farther  than  he  himself 
travels.  In  other  words, 
with  the  whirligig  there 
is  a  gain  in  the  distance 
that  the  boys  riding  on 
the  arms  are  moved. 
We  must  not  forget, 

however,   that  the  merry-    FlG-  2I4-     An  arrangement  that  gives  an 
,      .        ,  .  advantage  in  speed. 

go-round    is    heavier    to 

turn  when  one  pushes  on  the  arm  near  the  center 
than  when  the  pushing  is  done  at  the  end  of  the 
arm ;  that  when  we  gain  in  the  distance  we  move  an 
object,  we  do  so  at  the  expense  of  the  force.  But  with 
light  objects  we  are  willing  to  use  more  force  in  order 
to  move  them  rapidly,  and  we  have  many  machines 
that  are  designed  to  increase  the  speed  and  distance 
through  which  objects  can  be  moved. 

How  far  does  the  key  of  a  typewriter  move  when  it 
is  pushed  down?  How  far  does  the  type  move  when  it 
strikes  the  ribbon?  How  far  does  the  key  of  a  piano 
move,  and  how  far  does  the  hammer  travel  when  it  is 
thrown  against  the  string?  { 

Notice  that  the  type  and  the  hammer  move  through 
the  longer  distance  in  the  same  time  that  the  key  is 
moving  through  the  shorter  distance.  By  this  device 
the  velocity  of  the  type  and  hammer  is  greatly  increased, 
and  because  of  this  their  striking  force,  or  momentum 


356 


Science  for  Beginners 


FIG.  215.    Three  examples  of  levers. 

(page  221),  also  is  greatly  increased.  Thus  the  type 
makes  a  sharper  and  more  distinct  mark,  and  in  the  case 
of  the  hammer  even  a  slight  touch  of  the  finger  on  the 
key  produces  a  clear  and  distinct  sound. 

The  upper  pair  of  scissors  in  Figure  216  is  a  pair  of 
office  shears  for  cutting  paper.  Do  you  see  how  dis- 
tance is  gained  in  the  motion  of  the  blades? 

How  far  do  the  feet  move  in  making  a  revolution  on 
the  pedals  of  a  bicycle  ?  How  far  does  the  bicycle  move 
along  the  road  with  one  revolution  of  the  pedals?  Is 
it  easier  to  walk  or  to  ride  a  bicycle  up  a  hill  ?  Is  the 
bicycle  a  machine  for  gaining  force  or  for  gaining  distance  ? 

The  preceding  illus- 
trations have  shown 
that  there  is  a  second 
advantage  in  the  use 
of  machines :  we  can 
increase  the  distance 
an  object  is  moved, 
and  thus  move  a  light 
object  through  a  longer 
distance. 


FIG.  216. 


Aids  to  Our  Work 


357 


All  machines  combi- 
nations of  a  few  simple 
machines.  Since  we  so 
constantly  use  tools  and 
machinery,  it  is  very 
desirable  that  we  under- 
stand something  of  their 
action.  For  our  com- 
fort it  may  be  said  at 
once  that  almost  all 
machines,  no  matter 
how  complex,  are  only 
combinations  of  a  few 
very  simple  machines. 
These  simple  machines 
are  the  lever,  the  wheel 
and  axle,  the  pulley,  the 
inclined  plane,  the 
wedge,  and  the  screw. 

The  lever.  The  crow- 
bar is  a  good  example  of  a  lever,  the  most  commonly 
used  of  all  machines.  Notice  that  in  Figure  209  one  end 
of  the  crowbar  is  pushed  well  under  the  stone,  that  a 
smaller  stone  has  been  crowded  under  the  bar  quite 
near  the  stone  to  be  lifted,  and  that  the  man's  hand  is 
at  the  other  end  of  the  crowbar. 

The  point  where  the  bar  rests  on  the  smaller  stone  is 
called  the  fulcrum. 

The  force  applied  by  the  hand  or  in  any  other  way 
will  be  called  simply  the  force. 


FIGS.  217,  218,  and  219.    The  three  classes 
of  levers. 


358 


Science  for  Beginners 


FIG.  220.    What  two  advantages  are  gained  by  the  use  of  this  machine? 

Fig.  135.) 


(See 


The  part  of  the  lever  between  the  fulcrum  and  the 
hand  of  the  man  is  called  the  force  arm. 

The  weight  to  be  lifted  or  the  object  to  be  moved  is 
called  the  weight,  or  the  resistance. 

The  part  of  the  lever  between  the  fulcrum  and  the 
stone  that  is  being  lifted  is  the  weight  arm,  or  the  resist- 
ance  arm. 

Some  experiments  with  the  lever.  Arrange  a  lever 
for  yourself,  either  indoors  or  outdoors.  One  of  con- 
siderable length,  with  a  rather  heavy  weight,  will  be 
best.  Perform  the  following  experiments : 

Exercise  3.  Place  the  fulcrum  near  the  weight.  The  force 
arm  is  long  and  the  weight  arm  is  short.  Is  the  weight 
lifted  easily  ?  Which  moves  farther,  your  hands  or  the  weight 
you  are  lifting?  What  is  the  advantage  of  using  a  lever  of 
this  kind  ? 

You  will  notice  that  the  weight  moves  through  a  com- 
paratively small  distance  and  the  force  applied  moves 
through  a  much  greater  distance  in  the  same  time.  In 
other  words,  with  such  a  lever  we  use  a  small  force  through 


Aids  to  Our  Work  359 


FIG.  221. 


a  long  distance  and  move  a 
heavy  weight  slowly  through 
a  short  distance.  It  is  a  ma- 
chine by  the  use  of  which 
we  gain  in  force  at  the  ex- 
pense of  distance. 

Exercise  4.  Place  the  fulcrum  in  the  center  so  that  the 
force  and  weight  arms  are  of  the  same  length.  You  must 
now  apply  to  the  force  arm  a  force  equal  to  the  weight  of  the 
object  in  order  to  lift  it.  Which  moves  farther,  the  force 
or  the  weight  ? 

Would  you  gain  either  force  or  distance  by  the  use  of 
such  a  lever? 

Exercise  5.  Place  the  fulcrum  near  the  hands  so  that  the 
force  arm  is  short  and  the  weight  arm  long. 

Is  the  weight  lifted  easily  or  with  difficulty?  Does 
it  require  more  force  to  lift  it  this  way  or  to  lift  it  with 
your  hands?  Does  your  hand  or  the  object  you  are 
lifting  move  farther? 

With  a  lever  of  this  kind  we  may  use  great  force  slowly 
and  cause  a  small  body  to  move  rapidly.  In  other  words, 
with  such  a  lever  we  lose  in  force  but  gain  in  the  distance 
the  object  is  moved.  A  pair  of  pliers  or  the  sugar  tongs 
will  illustrate  this. 

These  experiments  have  shown  very  clearly  what  may 
be  called  the  law  of  the  lever ;  namely,  the  longer  tjie  force 
arm  in  comparison  with  the  weight  arm,  the  heavier  the 
weight  that  can  be  lifted,  but  the  shorter  the  distance 
through  which  the  weight  will  be  moved.  When  we  wish 
to  move  a  heavy  object  only  a  short  distance,  we  make  the 


360 


Science  for  Beginners 


FIG.  222. 


force  arm  long  and 
the  weight  arm  short. 
When  we  wish  to  move 
a  light  object  rapidly 
and  through  a  long  dis- 
tance, we  put  it  on  the 
end  of  a  long  weight 
arm  and  take  the  short 
force  arm  in  the  hand. 

Classes  of  levers.  There  are  three  classes  of  levers. 
When  the  fulcrum  is  between  the  force  applied  and  the 
weight,  we  have  a  lever  of  the  first  class.  The  levers  we 
have  used  in  our  experiments  are  all  of  this  class. 

When  the  weight  lies  between  the  fulcrum  and  the  force 
applied,  we  have  a  lever  of  the  second  class  (Fig.  218). 

In  levers  of  the  third  class  the  force  is  applied  between 
the  fulcrum  and  the  weight  (Fig.  219).  Levers  of  this 
class  all  gain  in  distance,  but  the  force  must  be  greater 
than  the  weight.  Study  Figure  219  and  see  if  you 
understand  why  this  must  be  true. 

Exercise  6.  Decide  whether  the  following  tools  are  levers 
of  the  first,  second,  or  third  class :  nutcracker,  a  pair  of  scis- 
sors, a  wheelbarrow,  the  oar  of  a  boat,  a  hammer  as  it  is 
used  in  pulling  a  nail,  a  hatchet  as  it  is  used  in  pulling  a 
nail,  a  pair  of  tongs,  the  forearm  of  a  man  (Fig.  215),  a 
pitchfork  as  it  is  used  in  pitching  hay. 

The  wheel  and  axle.  The  windlass,  the  capstan,  and 
the  steering  wheel  of  a  ship  are  good  examples  of  the 
wheel  and  axle.  They  are  all  special  forms  of  the  lever, 
and  work  according  to  the  same  principles.  This 


Aids  to  Our  Work 


361 


FIG.  223. 


you  will  readily  un- 
derstand if  you  will  con- 
sider the  crank  which 
turns  the  windlass  (F 
to  f)  the  force  arm, 
and  one  half  the  diam- 
eter of  the  windlass 
(/  to  W)  the  shorter 
weight  arm  (Fig.  210). 

It  is  evident  that  as  the  windlass  is  turned  about,  the 
hand  at  F  travels  much  faster  than  the  rope  is  wound 
up,  —  that  it  is  a  machine  by  which  we  lose  in  the  dis- 
tance through  which  the  object  is  moved,  but  a  machine 
which  gives  us  the  power  to  raise  a  heavier  weight  than 
could  be  lifted  without  it. 

What  force  would  be  necessary  to  lift  a  weight  of  300 
pounds  with  a  windlass  whose  axle  is  i  foot  in  diameter 
and  whose  handle  is  3  feet  long? 

Like  the  windlass,  the  capstan  is  a  lever,  and  because 
the  capstan  often  has  a  very  long  force  arm,  great  power 
can  be  secured  from  it.  The  great  length  of  the  force 
arm  explains  how,  by  the  use  of  the  capstan,  a  single  horse 
can 'draw  a  house  along  the  street  —  the  horse  travels 
many  feet  at  the  end  of  his  long  lever  while  the  house 
may  be  moved  only  a  few  inches. 

The  pulley.  There  are  two  kinds  of  pulleys,  the 
fixed  and  the  movable.  The  fixed  pulley  gives  us  no 
advantage  in  power  or  in  speed ;  it  only  changes  the 
direction  in  which  the  force  is  applied  (Fig.  225).  This 
kind  of  pulley  makes  it  possible  by  pulling  downward 


362 


Science  for  Beginners 


to  raise  a  bucket  of  water 
from  the  well,  and  for  the  horse, 
by  pulling,  to  lift  the  hay  to 
the  top  of  the  barn.  Do  we 
need  to  explain  the  advantage 
of  the  fixed  pulley  in  cases  like 
these?  Look  about  you  and 
find  other  cases  where  the  fixed 
pulley  is  used. 

The  movable  pulley  is  a  de- 
vice that  enables  us  to  gain  in 
force.  Examine  Figure  226 
and  you  will  see  that  the  hand 
supports  only  half  of  the  weight 
which  is  attached  to  the  block 
of  the  pulley.  Perhaps  you 
can  see  also  that  if  you  should 
draw  the  end  of  the  rope  a  foot  upward  the  pulley  and 
its  weight  would  rise  only  half  a  foot ;  the  lifting  force 
moves  through  twice  the  distance  that  the  weight  is 
raised.  A  pulley  of  this  kind,  therefore,  makes  it  pos- 
sible to  lift  twice  as  heavy  a  weight  as  can  be  raised 
without  it. 

Figure  227  shows  the  arrangement  of  what  is  known  as 
a  block  and  tackle.  The  pulley  blocks,  A  and  B,  make 
it  possible  to  use  as  many  pulleys  as  are  desired,  side  by 
side.  The  pulleys  in  A  are  fixed  and  those  in  B  are 
movable.  The  weight  to  be  lifted  is  attached  to  the 
block  B.  The  force  is  applied  to  the  loose  end  of  the 
rope,  which  is  first  attached  to  the  block  A  and  then 


FIG.  224.  Explain  how  the  course 
of  the  boat  is  determined  by  the 
movements  of  the  wheel. 


Aids  to  Our  Work 


363 


FIG.    225.     The   fixed  pulley  changes  the 
direction  in  which  the  force  is  applied. 


passed  successively  over  each  pulley 

in  both  blocks.     The  figure  shows  a 

system    of    2    movable 

and     3     fixed     pulleys. 

Notice  that  there  are  6 

ropes     supporting     the 

weight,     and     that    to 

shorten    each    of    these 

ropes  and  raise  the  boat 

i  foot  the  men  must  draw 

the    rope    downward    6 

feet.     By  this  system  every  pound  of  force  applied  will 

lift  6  pounds  of  weight,  but  what  we  gain  in  power  is 

lost  in  distance.     The  force  must  move  6  feet  to  raise 

the  weight  i  foot. 

The  inclined  plane.  If  a  barrel  of  flour  is  to  be  lifted 
into  a  wagon,  a  long  board  can  be  used,  with  one  end 
resting  on  the  wagon  and  the  other  upon  the  ground.  The 
barrel  of  flour  may  be  rolled  up  the  inclined  plane  thus 
formed.  The  man  or  boy  who  does  the  work  will  find 
that  he  can  do  it  much  more  easily  in  this  way  than  by 
lifting  the  barrel  directly  into  the  wagon. 

Any  inclined  surface  used  in  this  way  is  an  inclined 
plane.  A  road  running  up  the  side  of  a  hill  or  around 
a  mountain  is  an  example  of  an  inclined  plane.  It  is 
easier  to  climb  a  mountain  by  a  road  that  winds  about 
and  rises  gradually  than  to  go  straight  up  a  very  steep 
slope. 

The  law  of  the  inclined  plane.  This  law  is  the  same 
as  the  law  for  other  machines ;  the  longer  the  distance 


364 


Science  for  Beginners 


through  which  the  weight  is  moved,  compared  with  the 
height  it  is  lifted,  the  less  power  it  takes  to  do  the  work. 
For  example,  let  us  suppose  that 
a  man  wishes  to  load  a  barrel  of 
flour  which  weighs  200  pounds  into 
a  wagon  that  is  3  feet  high.  If  we 
do  not  count  the  friction  of  the  bar- 
rel, by  using  a  board  9  feet  long  he 
can  roll  the  barrel  into  the  wagon 
with  a  force  of  66f  pounds.  That 
is,  he  moves  the  barrel  through  3 
feet  of  space  to  lift  it  i  foot,  and  it 
will  take  only  |  as  much  force  to 
do  this  as  it  would  take  to  lift  the 
barrel  straight  up. 

The  wedge.  The  wedge  is  a 
machine  that  is  used  to  get  great 
sidewise  force.  It  tapers  gradually 
to  a  point,  and  as  it  is  driven  or 
pushed  forward,  the  thicker  part  of 
f'Vl;  A  ™vable  pul-  the  wedge  exerts  its  sidewise  pres- 

ley  doubles  the  lifting  power 

of  the  force.  sure.    Examine  Figure  230  and  you 

will  see  that  because  its  length  is 
greater  than  its  thickness,  the  wedge  travels  forward 
farther  than  it  pushes  the  two  sides  of  the  log  apart,  so 
that  we  are  here  gaining  in  force  and  losing  in  distance. 
In  reality,  the  wedge  is  simply  a  movable  inclined  plane, 
or  two  such  planes  joined  together  at  their  bases.  The 
force  applied  to  it  is  generally  a  blow  from  a  mallet  or 
hammer,  which  cannot  readily  be  measured,  so  that  it 


Aids  to  Our  Work 


365 


is  difficult  to  estimate  the  mechan- 
ical advantage  gained.  The  fric- 
tion to  be  overcome  is  very  great. 

Wedges  are  made  of  iron  or 
other  hard  material,  and  are  used 
for  splitting  logs  or  for  lifting 
heavy  weights  through  small  dis- 
tances. Leaning  chimneys  and 
masonry  walls  have  been  pushed 
into  an  upright  position  by  driv- 
ing wedges  in  on  the  lower  side. 
Nails,  needles,  pins,  knives,  axes, 
and  many  other  cutting  tools  are 
made  on  the  principle  of  the 
wedge.  We  use  the  sidewise  force 
from  these  tools  to  push  or  break 
apart  the  materials  we  are  work- 
ing on,  and  we  make  the  tools  thin 
at  the  edge  or  point  and  gradually 
thickening  so  that  we  shall  have 
the  mechanical  advantage  of  their 
pushing  forward  a  considerable 
distance  while  they  exert  a  side 
force  through  only  a  small  dis- 
tance. 

The  screw.    The  screw  is  a  com-  FlG-  22?-   The  lifting  P°wer 

...',,  of  the  force  is  multiplied  by  6. 

bmation  of  the  lever  and  the  in- 
clined plane.     In  the  jackscrew  (Fig.  231),  the  handle 
by  which  the  screw  is  turned  is  the  lever,  and  the  threads 
of  the  screw  are  the  inclined  plane  which  the  weight 


366 


Science  for  Beginners 


FIG.  228. 


slides  up .  When  the  force 
acting  on  the  end  of  the 
lever  has  made  one  revo- 
lution, the  weight  which 
rests  upon  the  top  of  the 
screw  has  evidently  been 
lifted  through  a  vertical 
distance  equal  to  the 
distance  between  the 
threads.  Has  the  hand  which  furnishes  the  power 
moved  much  farther  than  the  weight  has  been  lifted? 
For  what  purposes  are  jackscrews  used  ? 

The  most  common  example  of  a  screw  is  the  bolt  and 
nut.  Why  is  a  wrench  used  in  turning  a  nut  on  a  bolt? 
The  screw  press  and  the  vise  (Fig.  2  28)  are  other  examples  of 
the  screw.  Do  not  be  satisfied  by  merely  studying  about 
these  machines,  but  carefully  examine  a  bolt  and  nut; 
go  to  the  carpenter's  or  blacksmith's  shop  and  see  a  vise. 
An  excursion  to  the  railroad  station.  Stand  beside 
one  of  our  modern  railroad  engines  and  find  in  it  many 
of  the  simple  machines  you  have  just  studied.  Of  course 
you  knew  before  this  that  a  machine  is  not  simply  a 
device  for  making  use  of  the  power  in  a  man's  hand, 
but  also  a  means  of  utilizing  the  power  of  steam,  of  heat  or 
electricity,  of  running  water,  or  of  any  other  form  of  energy. 
What  is  the  force  applied  in  the  case  of  the  locomotive  ? 
Where  is  the  point  of  application  of  the  force?  What 
is  the  weight  or  resistance  to  be  overcome?  Note  the 
length  of  the  levers,  the  diameters  of  the  wheels  and 
axles,  and  other  features  of  this  powerful  machine. 


Aids  to  Our  Work 


36? 


FIGS.  229  and  230.    The  work  of  a  simple  but  very  powerful  machine. 

An  important  truth.  One  important  fact  about  machines 
should  be  clearly  understood.  No  machine  can  create 
or  increase  energy.  We  can  get  out  of  a  machine  only 
the  amount  of  work  we  put  into  it.  In  fact,  in  all 
machines,  some  energy  is  lost  by  the  friction  of  the  parts 
of  the  machine  upon  each  other.  The  lever  is  an  example 
of  a  machine  in  which  there  is  but  little  friction,  and  its 
efficiency  may  be  rated  as  nearly  looper  cent ;  on  the  other 
hand,  in  some  machines  the  efficiency  may  not  be  more  than 
60  per  cent.  By  the  word  efficiency  is  understood  the 
quotient  of  the  energy  regained,  called  the  useful  work, 
divided  by  the  total  energy  expended.  Thus : 

Effi  '  —  usefal  work  accomplished 

total  energy  expended 


368 


Science  for  Beginners 


FIG.    231.    A  combination  of  the  lever   and 
the  inclined  plane. 


A  que stion  to 
think  about.  If  a 
machine  cannot 
create  or  increase 
energy,  and  if  we 
must  do  as  much 
work  as  we  get  from 
it  —  or  even  more  — 
the  question  arises, 
What  are  the  advan- 
tages in  using  ma- 
chines, and  why  use 
them  at  all  ?  Several 
good  answers  to  this  question  can  be  given : 

(1)  Machines  enable  us  to  change  the  direction  of 
a  force  that  we  are  applying  to  our  work,  as  when  a 
load  of  hay  is  lifted  from  the  wagon  to  the  upper  part 
of  the  barn. 

(2)  They  enable  us  to  use  other  forces  than  our  own, 
as  when  we  use  the  horse   to   lift   the   hay   or   when 
the  energy  of  coal  or  falling  water  is  made  to  do  our 
work. 

(3)  By  means  of  a  machine  we  are  able  to  apply  power 
where  it  would  be  impossible    to   do   so  without  the 
machine.     We  can  draw  water  from  a  deep  well  by  a 
pump ;   we  can  sew  on  a  button  with  a  needle ;  with  an 
auger  we  can  bore  a  hole  in  a  piece  of  wood. 

(4)  Many  machines,  like  the  dynamo  and  the  steam 
engine,  make  it  possible  to  use  and  transform  one  form 
of  energy  into  another  form. 


Aids  to  Our  Work  369 

(5)  A  machine  enables  us  to  move  heavy  bodies  by 
the  use  of  a  small  force. 

(6)  It  is  possible  through  the  use  of  machines  and 
great  force  to  move  bodies  very  rapidly,  to  get  great 
speed  of  motion. 

Mention  other  great  advantages  derived  from  the 
use  of  machines. 


APPENDIX 


TABLE  OF  THE  MORE  COMMON  CHEMICAL  ELEMENTS,  WITH 
THEIR  SYMBOLS  AND  ATOMIC  WEIGHTS 


Aluminium  . . .  .  Al  27.1 

Antimony Sb  120.2 

Argon. A  39.88 

Arsenic As  74.96 

Barium Ba  137.37 

Bismuth .  Bi  208.0 

Boron B          n.o 

Bromin Br  79.92 

Cadmium Cd  112.40 

Calcium Ca  40.07^ 

Carbon C  12.00 

Chlorin Cl  35.46 

Chromium Cr  52.0 

Cobalt Co  58.97 

Copper Cu  63.57 

Fluorin. F  19.0 

Glucinum Gl          9.1 

Gold Au  197.2 

Helium He         4.00 

Hydrogen H  1.008 

lodin I  126.92 

Iridium Ir  193.1 

Iron Fe  55-84 

Krypton Kr  82.92 


Lead Pb 

Lithium Li 

Magnesium. . .  .Mg 
Manganese ....  Mn 

Mercury Hg 

Neon Ne 

Nickel Ni 

Nitrogen N 

Osmium. Os 

Oxygen O 

Phosphorus. .  .  .P 

Platinum Pt 

Potassium K 

Radium Ra 

Selenium Se 

Silicon Si 

Silver Ag 

Sodium Na 

Strontium Sr 

Sulfur S 

Tin Sn 

Tungsten W 

Uranium U 

Zinc..       .....Zn 


207.20 

6.94 

24.32 

54-93 
200. 6 

2O.2 
58.68 
I4.OI 
190.9 

16.00 
31.04 
195.2 
39.10 
226.0 
79.2 
28.3 
107.88 
23.00 
87.63 
32.06 
118.7 
184.0 
238.2 
65-37 


371 


INDEX 


A  star  (*)  after  a  page  number  indicates  that  an  illustration  of  the  subject  appears 
in  connection  with  the  reference. 


Accuracy,  necessary  in  the  scientist,  21. 

Acetic  acid,  58. 

Acids,  group  of  compounds  called,  57 ; 
importance  of,  in  industrial  processes, 
57;  study  of,  57-58;  properties  of, 
58-59 ;  neutralized  by  bases,  89- 
90;  salt  formed  by  neutralization 
of,  90-91.  , 

Agate,  a  variety  of  quartz,  152. 

Agricultural  classification  of  soil,  170- 
171. 

Agriculture,  use  of  science  in,  59,  174. 

Air,  water-holding  capacity  of,  63 ; 
study  of,  1 86  ff. ;  a  material  sub- 
stance, 186-187;  chemical  compo- 
sition of,  187-189;  nitrogen  and 
oxygen  in,  189-190;  percentage  of 
carbon  dioxid  in,  196-197;  argon 
in,  197 ;  water  vapor  in,  197 ; 
studied  in  connection  with  weather, 
198-216;  weight  of,  199-200;  pres- 
sure exerted  by,  2oo*-2O2*;  meas- 
uring pressure  of,  202-204 ;  cause  of 
rising  of,  207-208 ;  sound  trans- 
mitted by,  236-237. 

Air  globe,  199*. 

Alkali,  free,  in  soap,  119. 

Alkalinity,  litmus-paper  test  for,  89. 

Alum,  crystal  of,  81*. 

Amethyst,  a  variety  of  quartz,  152. 

Ammonia,  a  compound  of  nitrogen, 
194;  study  of,  194-195*;  com- 
mercial uses  of,  195 ;  experiment 
with,  195-196 ;  use  of,  in  ice  making, 
258-259. 

Ammonium  chlorid,  growth  of  yeast 
helped  by,  135. 

Animals,  water  in  bodies  of,  62. 

Anticyclones,  209*-2io. 

Antimony,  flame  test  for  compounds 
of,  1 1 6. 

Argon,  in  the  atmosphere,  197. 

Arsenic,  flame  test  for  compounds  of, 
116. 

"Ate,"  meaning  of  ending,  99. 

Atoms,  defined,  39. 


Bacteria,  nitrogen  taken  from  air  by, 
192-193  ;  dangers  of,  268-269. 

Baking  powders,  as  substitutes  for 
yeast,  135-138. 

Baking  soda,  example  of  a  base,  89; 
for  raising  bread,  136. 

Barium,  flame  test  for  salts  of,  116. 

Barometer,  use  of,  202,  203*;  law  of, 
203-204 ;  and  storm  center,  210-21 1 ; 
forecasting  weather  from  changes  of, 
211. 

Bases,  group  of  compounds  called,  57, 
89 ;  examples  of,  89 ;  properties  of, 
89 ;  neutralized  by  acids,  89-90 ;  salt 
formed  by  neutralization  of,  by 
acids,  90-91. 

Beaufort's  Scale,  205. 

Bleaching  powder,  made  from  chlorin, 
85  ;  disinfecting  water  by,  86. 

Block  and  tackle,  362-363,  365*. 

Bloodstone,  153. 

Blueprint  method  of  photography,  281. 

Bolt  and  nut,  366. 

Boron,  flame  test  for  compounds  of,  1 16. 

Bowlders,  glacial,  168*. 

Bread,  importance  of,  as  a  food, 
124;  how  to  study  making  of,  125- 
126;  definition  of,  126;  receipts  for, 
126-127;  importance  of  gluten  in, 
1 28-130 ;  baking  powders  for  raising, 
137-138;  self-rising,  138. 

Brine,  salt,  73. 

British  thermal  unit,  260-262. 

Brittleness,  a  property  of  matter,  33. 

Calcium,  flame  test  for  compounds  of, 
116;  amount  in  earth's  crust,  154*. 

Calcium  carbonate,  chemical  name  of 
limestone,  141. 

Calcium  oxid,  chemical  name  of  quick- 
lime, 142. 

Calcium  phosphate,  where  found,  97; 
manufacture  of  phosphorus  from,  97- 
98. 

Calorie,  unit  for  measuring  heat,  260- 
262. 


373 


374 


Index 


Cameo,  152*,  153. 

Camera,  invention  of,  272;  develop- 
ment of,  273*-28o*. 

Camera  obscura,  273*-274. 

Capstan,  example  of  wheel  and  axle, 
361*. 

Carbon,  in  turpentine,  56;  principal 
element  in  organic  substances,  100; 
compounds  of,  101-111. 

Carbonate  of  potash,  found  in  wood 
ashes,  116. 

Carbon  dioxid,  formation  of,  46-47; 
solvent  power  of  water  increased  by, 
67;  production  of,  107*-!  08;  test- 
ing for,  108-110;  produced  by  yeast 
in  bread  making,  132  ;  in  limestone, 
141 ;  percentage  of  atmosphere 
formed  of,  196-197. 

Carbon  disulfid,  composition  of,  55. 

Carnelian,  153. 

Caustic  soda,  89 ;  used  in  making  hard 
soap,  119. 

Caverns  in  limestone  regions,  147*. 

Cement,  made  from  forms  of  limestone, 
144,  146;  clay  used  in  making,  147. 

Centigrade  thermometer,  253-254*; 
invention  of,  257. 

Centimeters,  cubic,  262*. 

Chalcedony,  152. 

Chalk,  a  form  of  limestone,  144. 

Charcoal,  a  form  of  carbon,  101 ;  manu- 
facture of,  101-102*;  used  for  re- 
duction of  ores,  103  ;  same  chemical 
composition  in  diamond  and,  106. 

Charcoal  kiln,  102*. 

Chemical  action,  a  source  of  heat,  93  *, 
250;  electricity  produced  by,  315— 
316. 

Chemical  changes  in  matter,  38-39. 

Chemical  energy,  344*. 

Chemical  equations,  142. 

Chemical  formulas,  42. 

Chemical  symbols,  41-42. 

Chemistry,  science  known  as,  39; 
relation  of,  to  industrial  life,  80-8 1. 

Chile,  sodium  nitrate  fields  in,  190- 
191*. 

Chlorin,  an  element  of  salt,  78-79; 
preparation  of,  83*;  properties  of, 


84-85;  bleaching  powder  made 
from,  85  * ;  as  a  disinfectant,  86. 

Chrysoprase,  152. 

Classification,  necessary  in  science,  15 ; 
steps  in  process  of,  16;  importance 
of  wide  basis  of,  16-17;  of  outdoor 
objects,  17-18;  chronological  order 
in,  18;  alphabetical  order  in,  18-19. 

Clay,  used  in  cement,  147 ;  composi- 
tion of,  170-171. 

Clock,  working  of,  232*,  233. 

Clover,  tubercles  on  roots  of,  192*. 

Coal,  origin  of,  iio-m;  energy  in, 
345- 

Coconut  oil,  used  in  soap  making,  122. 

Coke,  production  of,  102 ;  used  for 
reduction  of  ores,  103. 

Cold,  a  relative  term,  252. 

Color  photography,  281. 

Colors,  in  solar  spectrum,  297 ;  quali- 
ties of  different,  299. 

Combustion,  49-50;  oxygen  a  sup- 
porter, nitrogen  a  non-supporter  of, 
189. 

Compass,  the,  300*;  mariner's,  301*; 
reason  for  pointing  north,  306-307. 

Compounds,  41 ;  different  from  ele- 
ments of  which  composed,  54-55; 
three  classes  of,  57. 

Conclusion,  formation  of,  in  scientific 
method,  5. 

Condenser,  35*. 

Conduction  of  heat,  247-248. 

Conservation  of  energy,  law  of,  346. 

Conservation  of  matter,  law  of,  35-36. 

Convection  of  heat,  247. 

Cookies,  receipt  for,  126. 

Copper,  malleability  of,  32 ;  ductility 
of,  32 ;  flame  test  for,  116. 

Copper  chlorid,  flame  test  for,  116. 

Copper  sulfate,  crystal  of,  82*. 

Coral  rock,  formation  of,  148. 

Cottonseed  oil,  used  in  soap  making, 
122. 

Cream  of  tartar,  for  raising  bread,  137. 

Crowbar,  example  of  lever,  350*,  357. 

Crystal  gazing,  151*. 

Crystals,  study  of,  81 ;  precious  gems 
as,  82;  rock,  151. 


Index 


375 


Cyclonic  storms,  204,  208-209*.  214*. 
215*,  216*. 

Definition,  defined,  24. 

Deflagrating  spoon,  47. 

Dextrin,  131. 

Diamond,  the,  105-106;    composition 

of,  io6*-io7. 
Dictionary,  use  of,  by  young  scientists, 

IQ-20. 

Disease  germs  in  water,  68-69 ;  killed 
by  chlorin,  86. 

Disinfectant,  chlorin  as  a,  86. 

Drift,  glacial  soils  called,  167;  com- 
position of,  168-169. 

Ductility,  a  property  of  matter,  32. 

Dynamite,  a  nitrogen  compound,  196. 

Dynamo,  electric,  used  as  an  electric 
motor,  328,  329*;  used  as  an  elec- 
tric generator,  332,  333*,  334;  im- 
portance of,  334-335- 

Earth,  elements  in  crust  of,  154*. 

Efficiency,  derived  from  machines,  350, 
367. 

Elasticity,  a  property  of  matter,  33- 
34- 

Electric  bell,  323,  324*,  325,  326. 

Electric  cells,  3i6*-3i9*;  terms  used 
in  connection  with,  319. 

Electric  iron,  322*. 

Electric  motor,  328,  329*,  330,  331. 

Electric  toaster,  322. 

Electricity,  a  source  of  heat,  251 ; 
production  of,  309 ;  early  history  of, 
309-310;  producing  static,  by  fric- 
tion, 310;  positive  and  negative, 
3 1 1-3 1 2 ;  like  kinds  of,  repelled 
and  unlike  kinds  attracted  by  each 
other,  312  ;  how  to  detect,  312-313  ; 
neutralization  of  positive  and  nega- 
tive charges  if  brought  together,  313 ; 
lightning  a  charge  of,  313-315; 
produced  by  chemical  action,  315- 
316;  the  voltaic  cell,  3i6*~3i7; 
the  gravity  cell,  317,  318*;  the 
Grenet  cell,  318*;  the  dry  cell, 

•  3i8*~3i9;  electroplating,  3i9*-32o; 
conductors  and  insulators,  320-321 ; 


resistance  to,  321 ;  applications  of, 
323-336;  energy  in,  343. 

Electromagnet,  307,  326-327,  329*, 
333*;  uses  of,  327. 

Electroplating,  3i9*-32o. 

Electroscope,  312*. 

Elements,  defined,  40-41 ;  use  of 
flame  test  to  find,  in  a  substance,  77 ; 
table  of,  371. 

Emerald,  the,  105  n. 

Energy,  meaning  of,  341-342;  differ- 
ent forms  of,  342-344 ;  transforma- 
tion of,  344-346 ;  conservation  of, 
346;  active,  or  kinetic,  and  stored, 
or  potential,  347-348;  not  created 
or  increased  by  machines,  367. 

Erosion,  process  of,  162. 

Ether  waves,  light  produced  by,  283 ; 
use  of,  in  wireless  telegraphy,  335; 
striking  qualities  and  uses  of,  335- 
336. 

Experiment,  scientific  method  of,  2. 

Eye,  the  human,  294-295*,  296*,  297*. 

Fahrenheit  thermometer,  253-254*; 
invention  of,  257. 

Farming,  use  of  sulfur  compounds  in, 
98;  potato  cultivation,  175-185. 

Feldspar,  crystal  of,  80*;  in  granite,  157. 

Fertilizers,  phosphates  as,  97;  ele- 
ments in  commercial,  194. 

Filtration  of  liquids,  75  *. 

Fire,  kindling,  by  chemical  action,  93*. 

Fireproofing  wood  of  matches,  99. 

Flame  test,  use  of,  77*;  for  detection 
of  metals,  115. 

Flatiron,  radiation  of  heat  from,  249*; 
electric,  322*. 

Flexibility,  a  property  of  matter,  34. 

Flint,  153. 

Flour,  used  in  bread  making,  126,  127  ; 
what  it  is,  127-128;  composed  of 
starch  and  gluten,  128;  starch  the 
•  principal  element  of,  130. 

Food,  amounts  of  water  in,  62. 

Fool's  gold,  158. 

Foot  pound,  339*- 

Force,  the  cause  of  motion,  225-226;  de- 
fined. 225  n. ;  of  gravitation,  226-227. 


376 


Index 


Formic  acid,  90. 

Fossils,  no*,  153*,  163. 

Franklin,  Benjamin,  experiments  of, 
with  electricity,  314-315. 

Freezing  mixtures,  256-257. 

Friction,  motion  destroyed  by,  222- 
223  ;  defined,  223 ;  rolling  less  than 
sliding,  223*,  224;  usefulness  of, 
224;  devices  to  lessen,  224*;  pro- 
ducing static  electricity  by,  310. 

Galileo,  first  law  of  pendulum  dis- 
covered by,  230-231. 

Galvanometer,  328. 

Gases,  23;  difference  between  solids, 
liquids,  and,  26-27;  sound  trans- 
mitted by,  237-238. 

Generator,  electric,  332-334. 

Geology,  science  of,  165. 

Gingerbread,  making  of,  136-137. 

Glacial  period,  167-168. 

Glaciers,  167-168. 

Glass,  brittleness  of  cold,  33  ;  ductility 
of  heated,  33*;  refraction  of  light 
by,  289-291. 

Gluten,  a  constituent  of  flour,  128; 
a  protein,  containing  nitrogen,  128; 
proportion  in  whole  wheat  flour  and 
in  fine  white  flour,  1 29 ;  importance 
of,  in  making  bread  rise,  129-130. 

Glycerin,  in  soft  soap,  118;  separation 
of,  from  hard  soap,  119. 

Glycerin  soap,  how  made,  1 20. 

Gold,  malleability  of,  31. 

Gold  chlorid,  use  of,  in  photography, 
277-280. 

Granite,  structure  of,  156*;  occur- 
rence and  uses  of,  158-159. 

Graphite,  104-105. 

Gravity,  force  of,  226*-227;  action 
of,  on  pendulum,  229. 

Gravity  electric  cell,  317,  318*. 

Grenet  electric  cell,  318*. 

Guncotton,  manufacture  of,  196. 

Hardness,  a  property  of  matter,  34. 
Hard  waters,  soap  test  for,  121-122. 
Heat,  solvent  power  of  water  increased 
by,  67 ;   capacity  of  soils  for  holding, 


172-173;  study  of,  242  ff. ;  water 
and  air  expanded  by,  243-244; 
what  it  is,  245-246 ;  why  expansion 
is  caused  by,  246-247 ;  convection 
and  conduction  of,  247-249 ;  radiant, 
249;  sources  of,  249-251;  a  rela- 
tive term,  252;  measuring  intensity 
of,  by  thermometer,  253-256;  re- 
quired to  evaporate  liquids,  257- 
258;  distinction  between  quantity 
of,  and  temperature,  259 ;  units 
for  measuring  quantity  of,  260-261 ; 
different  capacities  of  different 
substances  for  holding,  263-264; 
a  form  of  energy,  343. 

Heating  system,  hot-water,  245*,  246*. 

Heliotrope,  a  variety  of  quartz,  153. 

Horizon,  the,  165-166. 

Horse  power,  measuring  by,  340-341. 

Humus,  173-174. 

Hydrochloric  acid,  58,  59;  production 
of,  77;  uses  in  industries,  80; 
chlorin  obtained  from,  83 ;  flame 
test  for  compounds  of,  116. 

Hydroelectric  plant,  308*,  309. 

Hydrogen,  characteristics  of,  51-54; 
comparison  of  oxygen  and,  54;  in 
turpentine,  56;  decomposition  of 
water  into  oxygen  and,  70-7 1 ; 
affinity  of  chlorin  for,  84-85. 

Ice,  manufacture  of,  258*-259*. 

Iceland  spar,  80*,  140*. 

"Id,"  meaning  of,  as  an  ending,  49. 

Igneous  rocks,  159—161. 

Ignition  tube,  structure  of,  45  n. 

Illuminating  gas,  from  charcoal,  101, 
102;  from  coke,  102-103. 

Image,  formed  by  lens,  291-293. 

Immaterial,  matter  distinguished  from 
the,  22-23. 

Impenetrability,  a  property  of  all 
matter,  28 ;  meaning  of,  28-30. 

Incandescent  lamp,  321-322. 

Inclined  plane,  357,  363,  364 ;  law  of, 
363-364- 

Indestructibility,  a  property  of  mat- 
ter, 34-35. 

Induction,  magnetic,  304-305. 


Index 


377 


Ink,  made  from  lampblack,  104. 

lodin,  testing  starch  with,  130. 

Iron,  malleability  of,  32;  ductility  of, 
32;  reduction  of  ore,  103;  lime- 
stone used  in  manufacture  of,  144 ; 
magnet  attracts  and  is  attracted  by, 
303- 

Iron  pyrites,  158. 

Isobars,  212,  213. 

Isotherms,  212. 

"lum,"  meaning  of,  as  an  ending,  77. 

Jackscrew,  365-366,  368*. 
Jasper,  a  variety  of  quartz,  153. 

Kinetic  energy,  347  n. 

Lampblack,  103 ;  use  of,  104 ;  manu- 
facture of,  104*,  105*. 

Lava  fields,  160*. 

Lead,  flame  test  for  compounds  of, 
116. 

Legumes,  value  of,  191-192. 

Lens,  formation  of  image  by,  291-293  ; 
use  of,  in  magnifying  glass,  micro- 
scope, and  telescope,  293-294. 

Lever,  357;  parts  of,  357-358;  ex- 
periments with,  358-359 ;  law  of, 
359-360;  three  classes  of,  360; 
wheel  and  axle,  360-361 ;  pulley, 
361-363;  inclined  plane,  363-364; 
wedge,  364-365;  screw,  365-366. 

Light,  use  of,  in  photography,  271-272 ; 
nature  of,  282-283 ;  velocity  of, 
283;  and  motion,  283-284;  re- 
flection of,  284-287 ;  refraction  of, 
287-290;  action  on  human  eye, 
294-295 ;  dispersion  of,  297 ;  dis- 
persion of,  in  the  rainbow,  298- 
299 ;  action  of,  to  produce  differ- 
ent colors,  299;  length  of  ether 
waves  which  carry,  336;  a  form  of 
energy,  343. 

Lightning,  reason  for,  313-314*; 
Franklin's  experiment  with,  314- 
3i5- 

Lime,  example  of  a  base,  89 ;  produced 
from  limestone,  140-141,  144;  used 
for  sweetening  acid  soil,  194. 


Limestone,  carbon  found  in  beds  of, 
loo ;  study  of,  139  ff. ;  crystallized, 
139-140;  composition  of,  140; 
manufacturing,  143*- 144;  mortar 
and  whitewash,  144;  uses  and 
forms  of,  144;  caverns  caused  by, 
147*;  formation  and  occurrence  of, 
148;  used  for  sweetening  acid  soil, 
194. 

Limewater  test  for  carbon  dioxid,  108- 
110. 

Liquid  air,  23. 

Liquids,  23 ;  difference  between  solids, 
gases,  and,  26-27 ;  sound  trans- 
mitted by,  237-238;  heat  required 
to  evaporate,  257-258. 

Lithium,  flame  test  for  compounds  of, 
116. 

Litmus-paper  test,  of  acid,  57,  58,  59*; 
of  water,  88;  of  sodium  and  potas- 
sium, 88-89. 

Loam,  composition  of,  170-171. 

Lodestone,  302. 

Luray  Caverns,  147*. 

Lye,  made  from  wood  ashes,  116-117. 

Machines,  work  done  by,  341,  349  ff. ; 
denned,  350;  advantages  from  use 
°f>  356;  all  machines  combinations 
of  a  few  simple,  357 ;  energy  not 
created  or  increased  by,  367 ;  sum- 
mary of  advantages  of,  368-369. 

Magdeburg  hemispheres,  experiment 
with,  201-202*. 

Magnetic  field,  304. 

Magnetic  force,  304.         • 

Magnetic  needle,  300,  303*. 

Magnetic  poles,  306. 

Magnetite,  302. 

Magnets,  302-303 ;  bar  and  horseshoe, 
303;  poles  of,  304;  effect  of,  on 
one  another,  305-306;  producing 
electric  current  with,  331-332. 

Magnifying  glasses,  293. 

Malleability,  a  property  of  matter,  31 ; 
of  metals,  31-32. 

Mammoth  Cave,  147. 

Marble,  a  form  of  limestone,  140,  144. 

Mariner's  compass,  301*. 


378 


Index 


Marl,  composition  of,  145 ;  deposits  of, 
145 ;  measuring  amount  of,  in  a 
deposit,  146;  used  for  sweetening 
acid  soil,  194. 

Match,  early  substitutes  for,  92 ;  the 
primitive,  92-93;  invention  of  the 
friction,  94-95 ;  varieties  of  the 
friction,  95-96;  phosphorus  and 
sulfur  in,  96,  98;  and  fires,  98; 
fireproofing  wood  of,  99. 

Matter,  definitions  of,  22;  distin- 
guished from  the  immaterial,  22-23 ; 
gaseous,  liquid,  and  solid  forms  of, 
23 ;  division  of,  into  particles,  24 ; 
particles  composing,  called  molecules, 
25 ;  the  properties  of,  28-35  J  law 
of  conservation  of,  35-36;  temporary 
or  physical  and  permanent  or  chemi- 
cal changes  in,  37-39 ;  air  a  form  of, 
199-200;  and  motion,  217  ff. ;  un- 
able to  move  itself  or  stop  itself 
when  set  in  motion,  219-221. 

Mazda  lamp,  322. 

Measuring  by  the  scientist,  13-14. 

Metals,  malleability  of,  31-32;  ductil- 
ity of,  32;  sodium  and  potassium 
representative  of  rare  class  of,  86- 
87;  reduction  of  ores  of,  103; 
flame  test  for  detection  of,  115. 

Mica,  in  granite,  156;  qualities  of, 
157-158. 

Microscope,  principle  of,  293-294. 

Milky  quartz,  152. 

Mineral  deposits  about  mouths  of 
springs,  67-68. 

Minerals,  limestone,  139-148;  quartz, 
149-154;  difference  between  rocks 
and,  155. 

Mold  in  soil,  173-174. 

Molecules,  matter  composed  of,  25; 
defined,  25 ;  difference  in  condition 
of,  in  solids,  liquids,  and  gases,  26- 
27 ;  composed  of  atoms,  39 ;  heat 
due  to  motion  of,  246. 

Momentum,  denned,  221 ;  illustrations 
of,  222. 

Mortar,  chemical  changes  in,  144. 

Motion,  matter  and,  217*;  momen- 
tum, 221-222;  destroyed  by  fric- 


tion, 222-223;  tendency  of  moving 
body  to  travel  in  straight  line,  224- 
225;  to-and-fro,  or  vibratory,  228- 
234;  one  of  the  sources  of  heat, 
250;  produced  by  light,  283;  en- 
ergy of,  342-343- 
Motion  pictures,  281. 

Neutralization,  of  acids  by  bases,  89- 
91 ;  of  acid  soil,  193-194. 

Nitric  acid,  190;  nitrogen  com- 
pounds made  from,  196. 

Nitrogen,  contained  in  gluten,  128; 
proportion  of,  in  the  air,  189-190; 
an  inactive  element,  190;  com- 
pounds of,  not  plentiful,  190-191 ; 
lives  of  plants  and  animals  depend- 
ent on  compounds  of,  191 ;  drawn 
from  air  by  legumes,  191-192; 
keeping  supply  of,  in  soil,  194; 
ammonia  a  compound  of,  194-195 ; 
use  of  compounds  of,  in  war,  196. 

Nitroglycerin,  production  of,  119. 

Observation,  scientific  method  of,  2, 
4-5 ;  necessity  of,  to  the  scientist,  12. 

Onyx,  153. 

Opal,  154. 

Organic  matter  in  water,  68. 

Organic  substances,  carbon  principal 
element  in,  100. 

Oxidation,  slow,  40-50;  importance 
of  process  of,  50. 

Oxids,  compounds  of  oxygen  called, 
49. 

Oxygen,  abundance  and  activity  of, 
44 ;  preparing,  from  one  of  its 
compounds,  44—46*;  description  of, 
46;  activity  the  most  characteristic 
property  of,  48-49;  comparison  of 
hydrogen  and,  54;  decomposition 
of  water  into  hydrogen  and,  70-71 ; 
attraction  of  sodium  and  potassium 
for,  87;  amount  in  earth's  crust, 
154;  proportion  in  the  air,  189-190. 

Palisades    of    Hudson,     example    of 

igneous  rocks,  160,  161*. 
Pearls,  formation  of,  145. 


Index 


379 


Pendulum,  vibration  of,  228-230; 
laws  of,  230-232 ;  action  of,  in  a 
clock,  232*,  233. 

Petrified  wood,  153*,  154. 

Phosphate  deposits,  97. 

Phosphorus,  determining  presence  of, 
in  matches,  96;  where  found,  97; 
uses  of,  97;  manufacture  of,  97; 
poisonous  quality  of,  97-98;  care 
necessary  in  handling,  187-188. 

Photo-engraving,  281. 

Photography,  process  of,  271-272; 
definition  of,  272;  review  of  his- 
tory of,  272-277;  modern,  277-281. 

Physical  changes  in  matter,  38. 

Physics,  science  known  as,  38. 

Pipette,  130*. 

Platinum,  malleability  of,  31 ;  ductil- 
ity of,  32. 

Pliny,  on  soap  making,  112.    . 

Poles  of  magnet,  304. 

Portland  cement,  made  from  limestone, 
144;  value  of  marl  deposits  for, 
146;  clay  a  constituent  of,  147. 

Potash,  example  of  a  base,  89;  made 
from  wood  ashes,  117. 

Potassium,  a  rare  metal,  86;  attrac- 
tion for  oxygen,  87;  in  soap,  114, 
115,  116;  flame  test  for,  115. 

Potassium  carbonate,  in  wood  ashes, 
116. 

Potassium  hydroxid,  from  wood  ashes, 
117. 

Potato  bread,  receipt  for,  126. 

Potatoes,  use  of,  in  bread  making, 
133-134;  study  of,  175  ff. ;  are  en- 
largements of  underground  stems, 
175;  selecting  seed,  176-177;  test- 
ing quality  of,  177-178;  color  of, 
178-179;  texture  of  skin  of,  179; 
eyes  of,  179-180;  conditions  for 
producing  good,  180-184. 

Power,  defined,  340. 

Precious  stones,  105-106. 

Precipitate  of  carbon  dioxid,  109. 

Prism,  refraction  of  light  by,  289-290 ; 
dispersion  of  light  by,  296-297. 

Protein,  in  foodstuffs,  128;  testing 
for,  in  gluten,  128-129. 


Protoplasm,    bacteria    composed    of, 

268-269. 

Prussic  acid,  composition  of,  55. 
Pulley,     357 ;      fixed    and     movable, 

361-362;     block   and   tackle,    362- 

363,  365*. 
Pumice  stone,  used  in  scouring  soaps, 

122. 
Push  button,  electric,  324^3  2  6. 

Quartz,  properties  and  chemical  name 

of,  149-150;    varieties  of,  151-154; 

amount  in  earth's  crust,  154*;    in 

granite,  156-157. 
Quicklime,    production    of,    141-142; 

study  of,  142. 

Radiation  of  heat,  249. 

Radiometer,  283,  284*. 

Rain,  formation  of,  63-64.   See  Storms. 

Rainbow,  the,  297-299. 

Rainfall,  finding  annual,  64. 

Rain  gauge,  64,  206*. 

Reading  glass,  study  of,  290-291*. 

Recording  by  the  scientist,  15. 

Reduction,  process  of,  103. 

Reflection  of  light,  284;  laws  of,  285*, 
286*. 

Refraction  of  light,  287*-29o. 

Rochelle  salts,  137. 

Rock  crystal,  151. 

Rock  phosphate,  97. 

Rocks,  difference  between  minerals 
and,  155;  granite,  156-159;  igneous 
and  sedimentary,  159-163 ;  strati- 
fied, 163*;  fossils,  163;  sandstones, 
164;  shales,  164;  glacial,  168*; 
quality  of  residual  soils  dependent 
on,  170. 

Rose  quartz,  152. 

Rosin,  used  in  laundry  soap,  122. 

Rotation  of  crops,  184. 

Ruby,  the,  105  n. 

Rust,  37- 

Safety  match,  95-96. 

Salt,  composition  of,  55;  importance 
of,  7  2-73 ;  where  found,  73 ;  methods 
of  production,  73-74;  testing  solu- 


38o 


Index 


bility  of,  74-75 ;  physical  properties 
of,  75;  chemical  properties  of,  76; 
hydrochloric  acid  in,  77-78;  further 
composition  of,  78-79 ;  uses  in  in- 
dustries, 80-8 i. 

Salt  cake,  production  of,  80. 

Salts,  group  of  compounds  called,  57 ; 
formed  when  acid  and  base  neutral- 
ize each  other,  90-91 ;  most  numer- 
ous class  of  compounds,  91. 

Sand,  composition  of,  150,  170—171. 

Sandstones,  150,  159,  164. 

Saponification,  process  of,  123. 

Sapphire,  the,  105  n. 

Saturation  of  air,  63. 

Science,  denned,  i. 

Scientific  habit,  forming  the,  2. 

Scientific  method,  the,  2-3;  illustra- 
tions of,  3-11. 

Screw,  357,  367*;  principle  of,  365- 
366. 

Screw  press,  366. 

Sedimentary  rocks,  161-163. 

Sedimentation,  process  of,  162;  by 
alluvial  soil,  169-170. 

Shales,  159,  164. 

Silicified  wood,  153*,  154. 

Silicon,  amount  in  earth's  crust, 
154*. 

Silicon  dioxid,  chemical  name  of 
quartz,  150. 

Silver  chlorid,  use  of,  in  photography, 
276-280. 

Slates,  164. 

Sleet,  formation  of,  65. 

Smoke  paper,  how  to  make,  30  n. 

Smoky  quartz,  152. 

Snow,  formation  of,  64-65 ;  amount 
of  water  in,  65-66.  See  Storms. 

Snowflakes,  65*. 

Soap,  history  of  manufacture  of,  112- 
114;  chemical  composition  of,  114- 
117;  making  of,  117;  soft  soap, 
glycerin,  and  hard  soap,  117-119; 
free  alkali  in,  119;  toilet  soaps,  120; 
action  of,  on  skin,  120-121 ;  testing 
water  with,  121-122;  materials 
used  in  manufacture  of,  122. 
Soda,  example  of  a  base,  89. 


Soda  lye,  used  in  making  hard  soap,  119. 

Sodium,  an  element  of  salt,  77-78;  a 
rare  metal,  86-87 »  flame  test  for, 
US- 

Sodium  carbonate,  uses  of,  87. 

Sodium  hydroxid,  production  of,  89. 

Sodium  lactate,  136. 

Soil,  testing  of,  by  farmers,  59 ;  study 
of,  165  ff. ;  formation  of,  166-167; 
classification  of,  167 ;  glacial,  167- 
169;  alluvial,  169-170;  residual,  170; 
agricultural  classification  of ,  170-171 ; 
water-holding  capacity  of  different 
kinds  of,  I7i*-i72;  heat-absorbing 
capacity,  172-173;  vegetable  matter 
in,  173;  potatoes  and  the,  175  ff. ; 
most  suitable,  for  potatoes,  184; 
sweetening  acid,  193-194;  keeping 
supply  of  nitrogen  in,  194;  com- 
mercial fertilizers  for,  194. 

Soil  thermometer,  180*. 

Solar  salt,  74. 

Solar  spectrum,  296-297;  colors  in, 
297. 

Solids,  23 ;  difference  between  liquids, 
gases,  and,  26-27;  sound  trans- 
mitted by,  237-238. 

Solubility  of  substances,  74-75. 

Solvent  power  of  water,  66-67. 

Soot,  or  lampblack,  103. 

Sound,  study  of,  235  ff. ;  produced  by 
vibrations,  236;  transmitted  by  the 
air,  236-237 ;  transmitted  by  solids, 
liquids,  and  gases,  237-238;  de- 
fined, 238;  estimating  velocity  of, 
238-239 ;  pitch  of,  239-240 ;  musical, 
distinguished  from  noise,  240. 

Space,  cannot  be  occupied  by  two 
bodies  at  same  time,  30*. 

Spectacles,  use  of,  295-296. 

Stalactites,  67. 

Stalagmites,  67. 

Starch,  the  principal  element  of  flour, 
130;  use  of,  by  the  body,  131-132; 
percentage  of,  in  good  potatoes, 
177-178;  testing  potatoes  for,  178; 
cooking  of  foods  which  have,  178. 

Steam,  invisibility  of  real,  61. 

Storms,  definition  and  forms  of,  204; 


Index 


381 


production     of     model,      205-207 ; 

cyclonic,     208-209* ;     anticyclones, 

2o9*-2io;  movement  of,  210;  rain 

or  snow  at  center,  210;    barometer 

and  storm  center,  210-211 ;  maps  of, 

214*,  215*,  216*. 
Stratified  rocks,  163*. 
Strontium,  flame  test  for,  116. 
Sulfur,    determining    presence    of,    in 

matches,  96-97 ;    where  found,  98 ; 

deposits  of,  in  Louisiana,  98;    uses 

of,  98. 

Sulfur  dioxid,  made  from  sulfur,  98. 
Sulfuric    acid,    a    representative  acid, 

58;   action  of,  upon  salt,  76;   made 

from  sulfur,  98. 
Sun,   the  chief  source  of  heat,    251 ; 

the  source  of  light,  282 ;    the  great 

source  of  all  energy,  345-346. 

Tabulation  of  facts,  19. 

Telegraph,  wireless,  335. 

Telescope,  principle  of,  293-294. 

Temperature,  measuring,  252  ff . ;  dis- 
tinction between  quantity  of  heat 
and,  259;  practical  problems  con- 
cerning, 265-270. 

Temperature  graphs,  266. 

Thermograph,  266. 

Thermometer,  the,  253*;  Fahrenheit 
and  centigrade  scales,  253-256; 
practical  usefulness  of,  269-270. 

Thermometrical  problems,  265-270. 

Thunderstorms,  204. 

Tin,  malleability  of,  31-32. 

Tools,  349,  350*. 

Topaz,  false,  152.  • 

Tornadoes,  204. 

Turpentine,  a  study  of,  55-56;  car- 
bon and  hydrogen  in,  56;  results 
of  union  of  chlorin  and,  84. 

Turpentine,  oil  of,  composition  of,  55. 

Vegetable  matter,   in  water,   68;    in 

soil,  173. 
Verification,     step    of,     in     scientific 

method,  6. 

Vermilion,  composition  of,  55. 
Vibratory    motion,     228-234;     trans- 


verse,   longitudinal,    and    torsional, 
233-234;    sound  produced  by,    236. 

Vinegar,  a  representative  acid,  58. 

Viscidity,  129. 

Vise,  example  of  screw,  366,  368*. 

Volcanic  rocks,  159,  160. 

Volcanoes,  sulfur  from,  98. 

Voltaic  cell,  3i6*~3i7. 

Water,  composition  of,  42,  52 ;  a  study 
of,  60 ;  occurrence  of,  61-62 : 
amounts  of,  in  meat  and  other 
food,  62 ;  in  the  air,  63 ;  per  cent 
of  surface  of  earth  covered  by,  66; 
rain,  snow,  and  sleet,  63-66;  sol- 
vent power  of,  66-67 ;  organic 
matter  in,  68;  disease  germs  in, 
68-69;  chemical  composition  of, 
69-70;  decomposition  of,  into  hy- 
drogen and  oxygen,  70-71 ;  disin- 
fection of,  by  chlorin,  86;  soap 
test  for  hard,  121-122;  capacity  of 
soils  for  holding,  171-172;  heat- 
holding  capacity  of,  264;  refraction 
of  light  by,  287-289. 

Water  vapor,  steam  called,  61 ;  a 
part  of  the  atmosphere,  63,  197. 

Weather,  the,  198  ff. ;  what  is  meant 
by,  199;  storms,  204;  winds,  204- 
205 !  cyclones  and  anticyclones, 
208-210;  forecasting,  from  study 
of  barometer,  211;  study  of,  by 
Weather  Bureau,  21  i-2i 2 ;  studying 
the,  212-213. 

Weather  Bureau,  work  of,  211-212. 

Weather  maps,  214*,  215*,  216*. 

Weather  records,  26s*-266*. 

Wedge,  357,  367*;  principle  and  uses 
of,  364-365- 

Wheel  and  axle,  357;  examples  of, 
360-361. 

Whitewash,  chemical  changes  in,  144. 

Windlass,  example  of  wheel  and  axle, 
360,361*. 

Winds,  force  exerted  by,  204,  205; 
names  of,  205 ;  direction  of,  during 
and  after  storms,  213. 

Wireless  telegraph,  335. 

Wood,  silicified,  153*,  154- 


382 


Index 


Work,  defined,  337-338 ;  quantity  of, 
338 ;  time  and  effort  not  factors  in, 
338-339;  measurement  of,  330-341 ; 
done  by  machines  and  by  forces  of 
nature,  341 ;  energy  the  capacity  to 
do,  342;  machines  as  aids  to,  340- 
369- 

X-ray  photographs,  281. 

X-rays,  are  short  ether  waves,  336. 


Yeast,  used  in  bread  making,  126,  127; 
action  of,  132*;  temperature  suit- 
able for  growth  of,  133 ;  helping 
growth  of,  135;  baking  powders  as 
substitutes  for,  135-136. 

Yellowstone  National  Park,  68*, 
153*. 


Zinc,   flame   test 
116. 


for    compounds  of, 


Book  Notices 


NEW-WORLD     LANGUAGE 
SERIES  — SPANISH 

Lesson  Books :  Guillermo  Hall's  All  Spanish  Method,  First 
Book  ($1.00),  Second  Book  ($1.20),  or  in  one  volume  Complete 
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trated, especially  well  adapted  to  junior  high-school  classes. 

Readers :  Uribe's  Mexico  and  Phipps'  Paginas  Sudamericanas 
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INDIAN  LIFE  AND  INDIAN  LORE 
INDIAN  DAYS  OF  THE  LONG  AGO 

BY 

EDWARD  S.  CURTIS 
Author  oj  "The  North  American  Indian" 

Illustrated  with  photographs  by  the  author  and  drawings 
by  F.  N.  Wilson 


I 


N  this  book  the  author  gives  an  intimate  view  of 
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by  spiritual  beliefs  and  practices. 

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INDIAN  LIFE  AND  INDIAN  LORE 

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HEAD-HUNTERS 

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Author  of  "Indian  Days  of  the  Long  Ago" 
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style  of  the  true  epic. 

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